BFNA Title: Fontinalaceae-Fontinalis
Author: B. Allen
Date: February 22, 2010
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden

BFNA Web site: http://www.mobot.org/plantscience/BFNA/bfnamenu.htm

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XX. FONTINALACEAE Schimp., Coroll. Bryol. Eur. 96. 1856

Bruce Allen

Plants slender, medium-sized, or robust, forming loose or dense masses. Primary stems creeping. Secondary stems prostrate, pendent, or trailing, freely and irregularly branched; central strand absent; rhizoids on stems and at base of secondary stems, from initials abaxially to the leaf insertions and around secondary stem primordia; axillary hairs elongate. Leaves 3-ranked, keeled and conduplicate, concave, or plane; margins entire or serrulate; median leaf cells linear to linear-rhomboidal; alar cells firm-walled or enlarged and bulging; costa subpercurrent, percurrent, excurrent to long-excurrent or nearly absent. Sexual condition dioicous; perichaetia lateral on short branches. Seta short or elongate. Capsule immersed, laterally emergent, emergent or exserted, oval, oval-oblong, subcylindric or cylindric; stomata absent; operculum obtuse-conic, acute to obliquely rostrate; annulus rudimentary; peristome diplolepidous, exostome teeth 16, linear, sometimes united in pairs at tips, outer surface smooth and lightly thickened, inner surfaces heavily thickened, granulose, at times with obscure vertical striae, inner trabeculae heavily thickened, endostome segments linear, red to brownish-orange, papillose, joined by lateral bars only distally (trellis imperfect) or throughout (trellis perfect). Calyptra mitrate, long-conic, or long-cucullate, smooth, naked, sometimes clasping base of seta when young. Spores small or large, smooth to lightly papillose.

 

Genera 3, species 19 (3 genera and 15 species in the flora): North America, South America, Eurasia, Africa.

 

The family Fontinalaceae is distinguished by aquatic or semi-aquatic habitat, long axillary hairs, absence of stem central strand, lack of stomata, odd exostome morphology, and the unusual trellised endostome. The exostome teeth in the Fontinalaceae are linear with the outer and inner plates equally high. The Fontinalaceae endostome is firm rather than membranous because of relatively heavy secondary thickening. Secondary deposition is extremely localized and occurs primarily on the outer surface at and very near the wall pair sutures of the cells in the primary peristomial layer (PPL). Deposition on the inner surface occurs only where the cell walls of the inner peristomial layer (IPL) cells are contiguous to the secondary thickenings deposited by the PPL cells. The Fontinalaceae endostome also differs in its homogeneous structure; there is no division of the endostome into a basal membrane and segment/cilia complex. As a result, the Fontinalaceae endostome, or trellis, resembles a net consisting of 16 vertical filaments (each corresponding to the endostomial segment of a typical endostome) that are connected by nearly equidistant horizontal filaments.

When all the wall pair sutures in the PPL of a Fontinalaceae endostome are secondarily thickened, an unbroken net called a perfect trellis is formed. An imperfect trellis occurs when some wall pair sutures lack secondary thickening. Whether the trellis is perfect or imperfect, all trellises have 16 vertical filaments. Thus, imperfect trellises are formed when some (usually basal) horizontal wall pair sutures are unthickened. Furthermore, the vertical filaments of the Fontinalaceae endostome have median lines on both the front and back surfaces. In contrast, most moss endostomial segments have a median line only on the outside surface. A somewhat similar endostomial segment is seen in Funaria, Encalypta, Splachnum, Orthotrichum, Mittenia, and Timmia. The combination, however, of a firm endostome having a homogenous structure consisting of vertical filaments connected by equidistant horizontal filaments and vertical filaments with median lines on both surfaces is unique to the Fontinalaceae.

All three genera and most species of the Fontinalaceae are found in North America, making it the center of diversity for the family. Brachelyma, which is semi-aquatic, has a strong single costa, and occasionally stem paraphyllia, appears to be the basal genus in the family. Fontinalis, on the other hand, is generally aquatic, has a nearly absent costa, well-developed, often bulging alar cells, and immersed to shortly emergent capsules, and appears to be the most derived genus in the Fontinalaceae. The family seems closely related to Climacium on the basis of its primary/secondary stem structure, branching pattern, stem anatomy, single costae, and stem paraphyllia.

 

selected references  Cardot, J. 1892. Monographie des Fontinalacées. Mém. Soc. Sci. Nat. Cherbourg 28: 1--152. Welch, W. H. 1960. A monograph of the Fontinalaceae. M. Nijhoff. The Hague. Buck, W. R. and B. Allen. 1997. Ordinal placement of the Fontinalaceae. Cryptog. Bryol. Lichénol. 18: 227--234.

 

1. Leaves ecostate or nearly ecostate................................................... 3. Fontinalis, page XX

1. Leaves with long, single costa.

2. Leaves lanceolate or linear-lanceolate, slenderly acuminate, acute or obtuse; calyptra covering the capsule; seta 3--15 mm; capsules immersed, emergent or exserted......... 2. Dichelyma, page XX

2. Leaves oblong-lanceolate, gradually acute; calyptra covering only the operculum; seta 0.7--1.5 mm; capsules immersed................................................. 1. Brachelyma, page XX

 

3. FONTINALIS Hedwig, Sp. Musc. Frond., 298. 1801  [Latin, fons, fontis, spring or fountain, alluding to aquatic habitat]

 

Plants glossy, yellow-red, yellowish green, green, dark green, or brown. Primary stems creeping, secondary stems trailing, freely and irregularly branched, stem and branch tips elongate, slenderly and tightly attenuate or short and loose. Stems flaccid or rigid, in transverse section with epidermal cells somewhat enlarged, subepidermal cells small, thick-walled; central strand absent. Rhizoids on primary stems and at base of secondary stems, from clusters of initials abaxially to the leaf insertions, smooth, not or sparsely and irregularly branched. Leaves closely or distantly spaced, imbricate to erect-appressed when dry, erect to erect-spreading when wet, flaccid or firm, keeled and conduplicate, concave, or plane, ovate, oblong-ovate, oblong-lanceolate, ovate-lanceolate, lanceolate, narrowly lanceolate or linear, decurrent; apices acute, broadly acute or obtuse; margins at times broadly reflexed proximally, plane, erect, or involute at apex, entire proximally, entire to serrulate at apex; costa absent or nearly absent; median cells linear-fusiform to long-rhomboidal, firm-walled, smooth; alar cells enlarged, lax, bulging, subrectangular to oblong. Sexual condition dioicous; perigonia and perichaetia lateral on short branches. Seta short, smooth, cells quadrate to subrectangular. Capsule immersed to slightly emergent, ovoid to subcylindric; stomata absent; operculum conic to obtuse-conic; annuli rudimentary, consisting of several rows of small, thick-walled, horizontally elongated cells; peristome exostome teeth 16, linear, sometimes united in pairs at the tips, outer surface smooth and lightly thickened, inner surfaces heavily thickened, granulose, at times with obscure vertical striae, inner trabeculae heavily thickened, endostome trellis perfect or imperfect. Spores small or large, smooth to lightly papillose, sometimes of two sizes due to developmental abortions. Calyptra mitrate or long-conic, smooth, naked.

 

Species 13 (10 in the flora): North America, South America, Eurasia, Africa.

 

Fontinalis is characteristically aquatic or semi-aquatic. Many species can be found in seasonally dry habitats, but all are submerged in streams, lakes, ponds, pools, springs or seeps for a least part of the year. The genus exhibits remarkable gametophytic variability, perhaps due to the effects of seasonal wet/dry cycles as well as fluctuating parameters associated with an aquatic habitat. Morphological variability is high not only between populations but also within single collections of Fontinalis. The greatest amount of morphological variability is in species that normally are submerged only part of the year.

Plants of Fontinalis have creeping primary stems or stolons adnate to the substrate and indeterminate in growth. Secondary stems are often sparsely, irregularly branched and also indeterminate in growth; plants growing in shallow, permanently flowing streams can be over three feet long. Fontinalis is considered to have ecostate leaves, but the leaves have a multistratose basal region that has been interpreted as a rudimentary costa. Median leaf cells are long and narrow; the alar cells are often enlarged and inflated. Fontinalis has remarkably long axillary hairs; they can be over 900 \um. There are sporophytic character-complexes within Fontinalis that show meaningful taxonomic patterns at the species level, but, since the genus is dioicous, sporophytes are rarely encountered. Aquatic adaptations of sporophyte-associated features in Fontinalis include perigonia with few antheridia (1--2 or 4--6); enlarged, well developed vaginula; immersed or emergent capsules; very thick-walled capsules; lack of stomata; peristomes with endostomial trellises.

The taxonomy of Fontinalis is complicated by the small number of useful gametophytic character states found in the genus. In addition, because some important features of the genus are macroscopic, proper identification requires having large, healthy collections. Regrettably, success in keying out Fontinalis collections often depends on prior experience with the genus.

 

selected references  Allen, B. 1983. On the costa of Fontinalis (Musci). Lindbergia 9: 37--40. Allen, B. 1988. Studies on the genus Fontinalis (Musci: Fontinalaceae). Brittonia 40: 180--187. Allen, B. 1991. A review of the Fontinalis sullivantii complex (Musci: Fontinalaceae). Bryologist 94: 430--434. Allen, B. 1986--2008. Fontinalaceae Exsiccatae. Fasc. 1--6 (Nos. 1--174). St. Louis.

 

1. All or some stem leaves keeled and conduplicate.

2. Plants slender; leaves 2--4 mm.

3. Stems flaccid; branch and stem tips flaccid, short-attenuate; median leaf cells 4--8 \um wide; perichaetial leaves obtuse (gracilis-expression) 1. Fontinalis antipyretica, in part

3. Stems firm; branch and stem tips stiffly triangular, long-attenuate; median leaf cells 10--12 \um wide; perichaetial leaves apiculate to cuspidate 5. Fontinalis neomexicana

2. Plants medium-sized to robust; leaves 4--8 mm.

4. All leaves keeled; keels more or less curved the entire leaf length 1. Fontinalis antipyretica, in part

4. Stem leaves keeled or mostly keeled, branch leaves variously concave; keels more or less straight distal to the basal curve.

5. Branches with both keeled and concave leaves; branch and stem tips triangular, swollen, and flaccid (oreganensis-expression) 1. Fontinalis antipyretica, in part

5. Branches with only concave or tubular concave leaves; branch and stem tips concave, firm but loosely foliate 3. Fontinalis howellii

1. All leaves concave or flat.

6. All leaf apices with plane margins when wet.

7. Stem and branch tips tightly long-attenuate.

8. Plants with dimorphic leaves; stem leaves narrowly lanceolate to linear 9. Fontinalis sullivantii, in part

8. Plants with stem and branch leaves intergrading in size; stem leaves ovate-lanceolate, oblong-lanceolate, lanceolate, or linear-lanceolate.

9. Plants medium or large-sized, leaves flaccid, weakly concave or plane when wet (vernalis-expression) 8. Fontinalis sphagnifolia, in part

9. Plants slender, leaves firm, strongly concave when wet.

10. Leaves linear-lanceolate, proximal margins not reflexed when dry (aestivalis-expression) 8. Fontinalis sphagnifolia, in part

10. Leaves ovate-lanceolate to lanceolate, proximal margins usually reflexed when dry 2. Fontinalis dalecarlica, in part

7. Stem and branch tips short-attenuate or loosely foliate.

11. Leaves monomorphic; stem leaves ovate, ovate-lanceolate, oblong-lanceolate, or narrowly lanceolate 4. Fontinalis hypnoides

11. Leaves strongly dimorphic; stem leaves lanceolate to linear.

12. Stems flaccid; stem leaves 2--6(--9) mm, apices acute 9. Fontinalis sullivantii, in part

12. Stems stiff; stem leaves 6--9 mm, apices obtuse 7. Fontinalis redfearnii

 

6. Leaf apices with erect to incurved margins or a mixture of erect and plane margins when wet.

13. Plants medium to large-sized, leaves 0.7--2 mm wide, flaccid or firm, concave or plane when wet.

14. Stem and branch tips tightly long-attenuate, leaves usually flaccid, weakly concave with some plane leaves often present, leaf apices with margins when wet involute or plane; median leaf cells long-rhomboidal, 60--120 \um (vernalis-expression) 8. Fontinalis sphagnifolia, in part

14. Stem and branch tips usually loose and turgid, at times tightly short-attenuate; leaves firm, concave throughout, leaf apices with margins when wet consistently erect or involute; median leaf cells linear-fusiform, 80--180 \um 6. Fontinalis novae‑angliae

13. Plants slender, leaves 0.5--1.2 mm wide, firm, strongly concave when wet.

15. Branch leaves linear-lanceolate (aestivalis-expression) 8. Fontinalis sphagnifolia, in part

15. Branch leaves ovate-lanceolate to lanceolate.

16. Leaves not dimorphic; leaf apices plane or occasionally erect when wet; dry leaves usually flattened with narrowly reflexed margins; capsules immersed, ellipsoid to oval; perichaetial leaves acute or apiculate 2. Fontinalis dalecarlica, in part

16. Leaves weakly dimorphic; leaf apices consistently erect to incurved when wet; dry leaves without reflexed margins; capsules emergent, cylindric to subcylindric; perichaetial leaves broadly rounded 10. Fontinalis welchiana

 

1. Fontinalis antipyretica Hedwig, Sp. Musc. Frond., 298. 1801

 

Hypnum antipyretica Necker; Pilotrichum antipyretica (Hedw.) Müller Hal.; Fontinalis gigantea Sullivant; F. californica Sullivant; F. antipyretica var. robusta Cardot; F. antypyretica var. oreganensis Renauld & Cardot; F. mollis Müller Hal.; F. patula Cardot; F. allenii Cardot; F. utahensis Cardot & Thériot in Thériot

 

Plants medium to robust, to 40 cm, yellow-red, yellowish green, green, dark green or brown. Axillary hairs to 820 \um, of 6--10 cells, basal cell red, quadrate, distal cells hyaline, long-cylindric. Stems firm; stem and branch tips swollen, sharply angled. Leaves monomorphic, ovate, oblong-ovate, ovate-lanceolate, or suborbicular, 2--8 mm, erect to erect-spreading in 3 ranks when wet, imbricate to erect-appressed when dry, keeled and folded lengthwise, variously curved along the keel from the insertion to the apex; apices acute, broadly acute to rounded obtuse; margins occasionally broadly reflexed proximally on one side, entire proximally , entire to serrulate at apices; median cells 100--150 x 12--18 \um. Perigonial leaves 1.2--1.4 mm. Perichaetial leaves 2--3 mm, oval to suborbicular, obtuse, usually lacerated across the apex. Seta 0.2--0.3 mm. Capsule immersed to slightly emergent, ovoid to subcylindric, 2--2.7 mm; operculum obtuse-conic, 0.7--1.5 mm; endostome trellis perfect. Calyptra mitrate, 1.3--1.6 mm. Spores 14--20 \um.

 

Rocks, sticks, logs, roots in slow- or fast-moving streams, ponds, pools, ditches, swamps, and floodplains, seasonally dry; low to high elevations (0--3300 m); Greenland; St.Pierre and Miquelon; Alta., B.C., N. B., Nfld. and Labr., N.S., Ont., P.E.I., Que., Yukon; Alaska, Ariz, Calif., Colo., Conn., Del., Idaho, Ill., Maine, Mass., Mich., Minn., Mont., Nev., N.H., N.J., N.Mex., N.Y., Ohio, Oreg., Pa., R.I., S.Dak., Utah, Vt., Wash., Wis., Wyo.; Europe; n and s Africa; Asia; Atlantic Islands (Iceland).

 

Fontinalis antipyretica occurs in every conceivable habitat available to Fontinalis. In its typical form the plants are medium-sized, flaccid when dry, have three-ranked, conduplicate-keeled leaves curved along the keel line, and swollen stem and branch apices flaccid when dry. It is stenotypic in eastern North America where nearly all collections conform to the gigantea-expression. This expression differs from typical F. antipyretica in its robust size and very broad, closely overlapping leaves that are strongly curved along the keel line. The gigantea-expression is found throughout the range of the species and has an especially pronounced form in western North America nomenclaturally centered on F. mollis. Well-developed plants of the gigantea-expression are remarkably distinct, but there are collections that intergrade in every way with the typical form of the species. In addition, some collections have individual stems with leaves that switch back and forth between the two forms. The typical form of F. antipyretica is common in western North America, but the species is also extremely polymorphic there.

Most atypical western plants are variations on the oreganensis-expression: medium-sized plants; weakly keeled stem leaves that are straight to slightly bend along the keel line; apices frequently concave or plane and subobtuse or obtuse; branch leaves occasionally concave or plane. The oreganensis-expression is most common along the west coast, but also occurs sporadically throughout the range of the species. Fontinalis howellii and the oreganensis-expression of F. antipyretica at times intergrade; both have stem leaves with keels that are typically straight above the basal curve and concave branch leaves. Fontinalis howellii differs from the oreganensis-form in having larger plants; an abrupt transition from stem to branch leaf form; very long, slender branch leaves; and loosely foliate, terete stem or branch tips that when dry lack the swollen, triangular, appearance of the stem or branch tips in F. antipyretica.

The gracilis-expression is slender (leaves 2--4 mm), loosely foliate, with lax to flaccid stems and weakly keeled (often concave) leaves. It is similar to F. neomexicana in size and closely approaches the loosely foliate expression of that species. Fontinalis neomexicana differs in having firmer stems; more distinctly keeled leaves; narrower leaf cells (4--8 versus 10--12 \um wide); short-attenuate branch and stem tips; and apiculate to cuspidate perichaetial leaves.

Plants of F. antipyretica found in swiftly moving streams often have leaves completely split along the keel line, and can be mistaken for F. hypnoides (see e.g., Crum & Anderson, Mosses of North America 747).

 

2. Fontinalis dalecarlica Bruch & Schimper in Bruch, Schimper & Gümbel, Bryol. Eur. 5: 7. 1846 (fasc. 31)

 

Fontinalis squamosa Hedwig var. dalecarlica (Bruch & Schimper) Hartman

 

Plants slender, to 100 cm, dark-green to yellowish green, at times reddish. Axillary hairs 250--300 \um, 5--8 cells, basal cell red, quadrate, distal cells hyaline or reddish, long-cylindric. Stems rigid; stem and branch tips long, slender and tightly attenuate; rhizoids at base only. Leaves monomorphic, ovate-lanceolate to lanceolate, 2--4 mm, imbricate to subimbricate wet, flat with loosely reflexed margins dry, concave; apices acute or narrowly obtuse; margins erect to incurved at base, plane or erect to incurved at apex, serrulate or entire at apices; median cells 60--140 x 4--8 \um. Perigonial leaves 1--1.2 mm. Perichaetial leaves 2.8--3.2 mm, ovate to suboval, acute or apiculate, often lacerated across the apex. Seta 0.1--0.2 mm. Capsule immersed, ellipsoid to oval, 1.5--2.5 mm; operculum obtuse-conic, 1 mm; endostome trellis imperfect. Calyptra mitrate, 1.5--1.8 mm. Spores 20--50 \um.

 

Rocks and tree roots along or submerged in usually fast-moving streams, occasionally in pools, and lakes; low to high elevations (0--1524 m); Greenland; St.Pierre and Miquelon; N.B., Nfld and Labr., N.S., Ont., Que.; Ala., Conn., Ga., Ky., Md., Mass., N.H., N.J., N.Y., N.C., Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis.; w Europe.

 

Fontinalis dalecarlica is a slender species nearly always found in shallow, fast-moving streams. Wet plants typically are smoothly imbricate with long attenuate branch and stem tips; dry plants often have flattened leaves with strongly reflexed margins. These features are characteristic, but they appear to be accentuated by and correlated with strong stream currents. When found in fast-moving streams, the same features occur in F. neomexicana, F. novae-angliae, F. sphagnifolia, and F. hypnoides. Fontinalis dalecarlica has monomorphic leaves that vary from strongly concave throughout to concave proximally and plane distally. Apical leaf margins are usually plane, but on strongly concave leaves they can be erect.

The slender size and concave leaves of F. dalecarlica distinguish it from all other members of the genus except F. welchiana, F. sphagnifolia (aestivalis-expression), and rigid forms of F. sullivantii. In size, aspect, and branch leaf form F. welchiana and F. dalecarlica are identical. Fontinalis welchiana, however, typically occurs in seasonally dry streams, has weakly dimorphic leaves (large subflaccid stem and small, rigid, strongly concave branch leaves), and leaves with consistently erect to incurved apical leaf margins. Fontinalis welchiana also differ from F. dalecarlica in emergent, cylindric to subcylindric capsules and broadly rounded perichaetial leaves. The aestivalis expression of F. sphagnifolia is similar to F. dalecarlica in having long-attenuate branch and stem tips as well as branch leaves that are strongly concave when wet. It differs from F. dalecarlica in having long, linear-lanceolate leaves. Fontinalis sullivantii differs from F. dalecarlica in having strongly dimorphic, linear-lanceolate stem and branch leaves with consistently plane apical leaf margins. When dry the leaves in F. neomexicana collections from fast-moving streams often resemble those of F. dalecarlica because they are plane rather than keeled, but when wet the leaves are strongly keeled.

Large plants of Fontinalis dalecarlica sometimes approach those of F. novae-angliae in size, and the two species are often confused. In addition to its larger size (stem leaf width: 0.7--2 versus.0.5--1.2 mm), F. novae-angliae lacks long-attenuate stem and branch tips, and its leaves have consistently erect to incurved apical margins. It further differs from F. dalecarlica in having oval to suborbicular, obtuse perichaetial leaves; rhizoids at multiple insertions along the stem; subcylindric to cylindric capsules; and smaller spores (12--18 \um). All reports of F. dalecarlica from Alberta, Saskatchewan, and Manitoba are slender forms of F. hypnoides.

 

3. Fontinalis howellii Renauld & Cardot, Bot. Gaz. (Crawfordsville) 13: 200. 1888

 

Fontinalis kindbergii Renauld & Cardot; F. chrysophylla Cardot

 

Plants medium to robust (rarely slender), to 35 cm, reddish, yellow-red, golden brown, to pale-green. Axillary hairs 600--750 \um, 6--10 cells, basal cell red, quadrate to short-rectangular, distal cells hyaline, long-cylindric. Stems firm; stem and branch tips firm and loosely foliate, terete, not angled. Leaves strongly dimorphic. Stem leaves ovate-lanceolate to lanceolate, 4--7 mm, erect to erect-spreading, loosely ranked wet or dry, sharply or weakly keeled and folded lengthwise, keels straight above the basal curve; apices acute to narrowly obtuse; margins plane, at times erect to somewhat involute at apices, entire proximally, entire to serrulate at apices; median cells 110--180 x 12--16 \um. Branch leaves lanceolate to linear-lanceolate, 3--6 mm, erect-spreading when dry, spreading and sharply 3-ranked when wet, concave to tubular-concave, not keeled; apices long-acuminate, acute to somewhat rounded; margins involute. Perigonial leaves 0.7 mm. Perichaetial leaves 2--3 mm, oval to suborbicular, obtuse, usually lacerated across the apex. Seta 0.2--0.3 mm. Capsule immersed to slightly emergent, oblong to subcylindric, 2.0--2.5 mm; operculum conic, 1 mm; endostome trellis perfect. Calyptra mitrate, 2 mm. Spores 12--16 \um.

 

Logs, sticks and shrubs in swamps, pools, and ponds, in streams, streamlets, or springs, wet rocks in seeps, often seasonally dry; low to high elevations (3--1628 m); B.C.; Calif., Idaho, Mont., Oreg., Wash.

 

Fontinalis howellii is typically a medium to robust species found mostly in pools, ponds, or slow-moving water, often in seasonally dry habitats, at times in association with Dichelyma. Wet plants characteristically have spreading, sharply 3-ranked branch leaves; when dry the branch and stem tips are firm, loosely foliate, and terete. The typical form of F. howellii differs from all other keeled species of Fontinalis in having strongly heteromorphic leaves: stem leaves keeled-conduplicate; branch leaves concave to tubular-concave. The change from stem to branch leaf form is remarkably abrupt; transitional leaf forms are almost always absent. Also distinctive are its stem leaves with straight keels after the basal curve, and linear-lanceolate to lanceolate branch leaves. Plants that grow permanently submerged (chrysophylla-expression) differ from the typical form in their smaller size and in having mostly concave stem leaves.

The oreganensis-expression of Fontinalis antipyretica and F. howellii at times intergrade; both have stem leaves with keels that are typically straight above the basal curve and concave branch leaves. The oreganensis-expression differs from F. howellii in often having smaller plants; some transitional leaves between the typical stem and branch leaf forms; shorter, broader branch leaves; and triangular branch and stem tips that when dry have a swollen aspect very different from the firm, loosely foliate, branch and stem tips in F. howellii. All collections referred to F. howellii from eastern North America and recent reports from Germany represent the oreganensis-expression of F. antipyretica. The only other Fontinalis taxon with tubular-concave leaves is the cymbifolium-expression of F. novae-angliae. It differs from F. howellii in having consistently concave stem leaves.

 

4. Fontinalis hypnoides Hartman, Handb. Skand. Fl. (ed. 4) 434. 1843

 

Fontinalis duriaei Schimper; F. nitida Lindberg & Arnott; F. tenella Cardot; F. dalecarlica var. macounii; F. mac-millanii Cardot; F. holzingeri Cardot in Holzinger; F. obscura Cardot in Holzinger; F. umbachii Cardot; F. subcarcinata Cardot; F. nitida var. angustiretis Cardot ex W. H. Welch. in Grout

 

Plants slender to medium-sized, to 30 cm, green, yellowish green, or pale green. Axillary hairs to 800 \um, 6--10 cells, basal cell red, quadrate, distal cells hyaline or reddish, long-cylindric. Stems flaccid, stem and branch tips loose, occasionally tightly attenuate. Leaves typically widely spaced, spreading, ovate, ovate-lanceolate, lanceolate, narrowly lanceolate to linear-lanceolate, 3--7 mm, flaccid dry, plane or subconcave at base, apices broadly acuminate, acute or subobtuse, occasionally twisted at the apices; margins plane or erect proximally, plane at apices, entire to serrulate at apex; median cells 80--150 x 8--15 \um. Perigonial leaves 0.6--0.8 mm. Perichaetial leaves 1.8--2 mm, oval to suborbicular, obtuse, usually lacerated across the apex. Seta 0.25--0.3 mm. Capsule immersed to slightly emergent, oval, suboval or oblong, 1.5--2.5 mm; operculum obtuse-conic, 0.8--1.2 mm; endostome trellis perfect. Calyptra mitrate, 1.2--1.5 mm. Spores 13--20 \um.

 

Rocks, boulders, base of trees, roots, sticks in streams, swamps, lakes, or ponds; low to high elevations (6--2800 m); Alta., B.C., Man., N.B., N.W.T., N.S., Ont., Que., Sask., Yukon; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nev., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., S.Dak., Tex., Utah, Vt., W.Va., Wis., Wyo; Europe; n Asia.

 

Fontinalis hypnoides is separated from all other Fontinalis species by medium size and monomorphic leaves consistently plane at the apices. It is typically found in slow-moving to sluggish streams and ponds. Critical features of the species in this habitat include flaccid stems with well-spaced leaves that are plane or subconcave only at the very base and have enlarged, distinctly differentiated alar cells. Plants from fast-moving streams differ from the typical form in having stiffer stems with closely spaced leaves that are subconcave to concave in the lower half and sometimes have reflexed margins when dry. Leaf shape in F. hypnoides is extremely variable: ovate to ovate-lanceolate (duriaei-expression); lanceolate to narrowly lanceolate (hypnoides-expression); linear-lanceolate (tenella-expression). Extreme expressions are sometimes recognized at the species level; but so many collections have leaves with intermediate forms that the group is best treated as an intergrading series of expressions. A particularly distinctive expression often found in the northern Great Lakes area (mac-millanii-expression) has subconcave, ovate-lanceolate leaves that are often twisted at the apices.

Flaccid forms of F. hypnoides can be difficult to separate from F. sphagnifolia (vernalis-expression) which is similar in size, has monomorphic leaves, and at times flaccid stems with mostly plane leaves. Plants of F. sphagnifolia differ from those of F. hypnoides in having tight, long-attenuate branch and stem tips, and a mixture of leaf apices with plane or erect to incurved margins. Stiff forms of F. hypnoides can resemble F. novae-angliae, but that species has leaf apices with erect to incurved margins. Both stiff and flaccid forms of F. hypnoides are sometimes confused with F. sullivantii which also has stiff and flaccid forms, well-spaced, plane to subconcave leaves, and consistently plane leaf apices. Fontinalis sullivantii always has linear-lanceolate stem leaves and most of its forms differ from F. hypnoides in their considerably smaller size. All collections of F. sullivantii differ from F. hypnoides in having strongly dimorphic stem and branch leaves. Fontinalis redfearnii and F. hypnoides (tenella-expression) are similar in aspect and have linear-lanceolate leaves with plane apical margins. Fontinalis redfearnii, however, has strongly dimorphic leaves and longer stem (6--9 mm) leaves.

 

5. Fontinalis neomexicana Sullivant & Lesquereux, Musci Bor.-Amer. 47 [no. 224b]. 1856 [1857]

 

Fontinalis mercediana Lesquereux; F. maritima Müller Hal.; F. columbica Cardot

 

Plants slender to medium, to 50 cm, pale-green, green, yellowish green, or golden brown. Axillary hairs 300--450 \um, 5--7 cells, basal cell red, quadrate, distal cells hyaline, long-cylindric. Stems firm; branch and stem tips imbricate, long-attenuate, sharply 3-angled. Leaves monomorphic, oblong-lanceolate to ovate-lanceolate, 2--4(--5) mm, erect, erect-spreading in 3 ranks when wet, erect-spreading to spreading when dry, keeled and folded lengthwise, keel straight or moderately curved above basal curve, occasionally strongly curved; apices acute, occasionally subobtuse; margins at times loosely reflexed when dry, plane when wet, entire throughout, occasionally serrulate at apices; median cells 120--180 x 4--8 \um. Perigonial leaves 1.3--1.5 mm. Perichaetial leaves 3--3.5 mm, oval to suborbicular, abruptly apiculate to cuspidate, at times lacerated across apex. Seta 0.2--0.3 mm. Capsule immersed to slightly emergent, ovoid to oblong, 2--2.5 mm; operculum obtuse-conic, 0.6--0.9 mm; endostome trellis perfect. Calyptra mitrate, 2 mm. Spores 15--25 \um.

 

Rocks and boulders, rarely sticks, swift or occasionally slow streams; low to high elevations (0--3353 m); Alta, B.C.; Alaska, Calif., Colo., Idaho, Mich., Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo.

 

Fontinalis neomexicana is a slender species with monomorphic, keeled leaves, very narrow leaf cells, and mostly entire leaf margins. Leaf keels above the basal curve vary from nearly straight to moderately curved. Apiculate to cuspidate perichaetial leaves are a diagnostic feature of the species. Fontinalis neomexicana is often found in shallow, fast-moving streams. In this habitat wet plants are typically triangularly imbricate with firm, long attenuate, sharply 3-angled branch and stem tips; dry plants often have erect-spreading to spreading, distinctly 3-ranked leaves with loosely reflexed margins. These features appear to be accentuated by and are correlated with strong stream currents. Dry plants with loosely reflexed leaf margins are also associated with fast-moving stream habitats in F. dalecarlica, F. novae-angliae, F. sphagnifolia, and F. hypnoides. In slow-moving streams, F. neomexicana has loosely foliate stems and somewhat lax, shortly attenuate branch and stem tips.

The imbricate foliate form of F. neomexicana is similar in size and aspect to F. dalecarlica; both species have attenuate branch and stem tips. They are sometimes confused because the dry leaves of F. neomexicana can appear to be concave rather than keeled. Wet plants of F. neomexicana differ from F. dalecarlica in having keeled leaves and angled rather than terete branch and stem tips. Slender forms of F. antipyretica (gracilis-expression) closely approach the loosely foliate form of F. neomexicana; the slender forms of F. antipyretica, however, have lax to flaccid stems; weakly keeled (often concave) leaves; broader leaf cells (10--12 vs. 4--8 \um wide), short, swollen branch and stem tips; and obtuse perichaetial leaves.

 

6. Fontinalis novae-angliae Sullivant, Musci Hepat. U. S. (repr.) p. 104. 1856

 

Fontinalis lescurii Sullivant var. cymbifolia Austin; F. novae-angliae Sull. var. cymbifolia (Austin) W. H. Welch in Grout; F. delamarei Renauld & Cardot; F. involuta Renauld & Cardot in Cardot; F. waghornei Cardot

 

Plants medium-sized to robust, green, yellowish green, reddish green to brownish. Axillary hairs 500--650 \um, 5--8 cells, basal cell red, quadrate, distal cells hyaline or reddish, long-cylindric. Stems stiff to firm; stem and branch tips swollen, not or slightly attenuate. Leaves monomorphic, ovate, ovate-lanceolate, or oblong-lanceolate, 2.5--5.5 mm, erect to imbricate wet, concave to tubular-concave; apices acute to subtruncate; margins erect or plane at base, erect to incurved at apex, serrulate or occasionally entire at apices; median cells 80--180 x 8--15 \um. Perigonial leaves 1--1.2 mm. Perichaetial leaves 2.4--2.8 mm, oval to suborbicular, obtuse, usually lacerated across apex. Seta 0.1--0.3 mm. Capsule immersed to slightly emergent, subcylindric to cylindric, 1.5--2.5 mm; operculum obtuse-conic, 1 mm; endostome trellis imperfect to subperfect. Calyptra mitrate, 1.2--1.5 mm. Spores 12--18 \um.

 

Rocks, boulders, and roots in ponds, lakes, streams and rivers, at times in summer dry streams; low to medium elevations (3--600 m); N.B., Nfld. and Labr. (Nfld), N.S., Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ky., La., Maine, Md., Mass., Miss., N.H., N.J., N.Y., N.C., Okla., Pa., S.C., Tenn., Tex., Vt., Va., W.Va.

 

Fontinalis novae-angliae is a medium-sized to robust species typically found in slow-moving streams, lakes or ponds. It has swollen to slightly attenuate branch and stem tips, and monomorphic, ovate-lanceolate to oblong-lanceolate leaves with consistently erect to involute apical margins. Dry plants typically have concave leaves, but plants from fast-moving streams sometimes have flat leaves with narrowly reflexed margins when dry. There are two distinct expressions of F. novae-angliae. The type-expression has somewhat lax plants with well-spaced, broad, moderately concave leaves. In the cymbifolium-expression the plants are stiff with closely spaced, narrow, tubular-concave leaves.

Fontinalis howelli is the only other species in the genus with tubular-concave leaves. In that species, however, the branch leaves are tubular-concave but the stem leaves are keeled-conduplicate. Fontinalis novae-angliae has been chronically confused with F. sphagnifolia. The two species are often similar in size and leaf shape, but F. sphagnifolia is a morphologically complex species with two remarkably distinct forms: the vernalis-expression and the aestivalis-expression. Both forms of F. sphagnifolia differ from F. novae-angliae in having long, tightly attenuate stem and branch tips. The vernalis-expression of F. sphagnifolia further differs in flaccid leaves with apical margins that are sometimes erect to incurved and other times plane. The aestivalis-expression has firm, strongly concave leaves similar in form to those of the cymbifolium-expression of F. novae-angliae, but differs in having distinctly smaller, slender plants with linear-lanceolate leaves.

Fontinalis dalecarlica and F. novae-angliae have often been confused because they both have firm, concave leaves. But F. dalecarlica is a slender species with narrow leaves (stem leaves 0.5--1.2 versus 0.7--2 mm wide) that usually have plane apical leaf margins when wet and reflexed proximal leaf margins when dry. In addition the stem and branch tips of F. dalecarlica are typically long-attenuate; the perichaetial leaves are acute or apiculate; the capsules are immersed, ellipsoid to oval; and the spores are larger (20--50 versus 12--15 \um).

 

7. Fontinalis redfearnii B. H. Allen, Bryologist 94: 201. 1991

 

Plants robust, to 15 cm, dark-green to yellowish green. Axillary hairs 740--918 \um, 8--12 cells, basal 1--2 cells reddish brown, short-rectangular, distal cells hyaline, becoming red with age, long-cylindric. Stems rigid; stem tips loosely foliate. Stem and branch leaves dimorphic, differing greatly in size. Stem leaves long, narrowly lanceolate to linear, 6--9 mm, distantly spaced, erect-patent dry, stiffly patent to spreading wet, firm, concave at base, plane; apices broadly obtuse; margins plane at apex, entire proximally, entire to serrulate at apex; median cells 80--160 x 8--12 \um. Branch leaves 3--4 mm, concave, apices acute to obtuse. Sporophytes unknown.

 

Base of Taxodium, rocks; medium elevation (243 m); Okla.

 

Fontinalis redfearnii is separated from other members of Fontinalis by its robust size; distantly spaced leaves; loosely foliate stem tips; strongly dimorphic branch and stem leaves; and narrowly lanceolate to linear-lanceolate stem leaves that have broadly obtuse, consistently plane apices. Three other Fontinalis species with wide-spaced, narrowly lanceolate leaves with plane apices can be confused with F. redfearnii: F. hypnoides (tenella-expression), F. sphagnifolia (vernalis-expression), and F. sullivantii. Fontinalis hypnoides (tenella-expression) differs from F. redfearnii in having flaccid to somewhat stiff stems and smaller (5--7 mm), monomorphic leaves. F. sphagnifolia (vernalis-expression) differs most clearly from F. redfearnii in having tight, long-attenuate branch and stem tips. In addition, it has flaccid stems, weakly dimorphic leaves, and a mixture of leaf apices with plane or erect to incurved margins. Fontinalis sullivantii is the only other Fontinalis species with strongly dimorphic leaves. Although F. sullivantii typically differs from F. redfearnii in having much smaller plants and flaccid stems, there are robust, stiff forms of the species that closely approach F. redfearnii. All forms of F. sullivantii, however, differ from F. redfearnii in narrower leaves with acute apices.

 

8. Fontinalis sphagnifolia (Müller Hal.) Wijk & Margadant, Taxon 11: 221. 1962

 

Pilotrichum sphagnifolium Müller Hal., Syn. Musc. Frond. 2: 150. 1850; Fontinalis biformis Sullivant in A. Gray; F. lescurii Sullivant in A. Gray; F. eatoni Sullivant ex Sullivant & Lesquereux; F. lescurii var. ramosior Sullivant; F. frostii Sullivant in Cardot; F. novae-angliae var. cardotii Renauld in Cardot; F. cardotii (Renauld in Cardot) Cardot; F. novae-angliae var. heterophylla Cardot in Nichols; F. novae-angliae var. latifolia Cardot in Nichols; F. novae-angliae var. groutii W. H. Welch in Grout

 

Plants slender, medium-sized, or robust, to 60 cm, green, yellowish green, reddish green or brownish. Axillary hairs 500--650 \um, 5--8 cells, basal cell red, quadrate, distal cells hyaline or reddish, long-cylindric. Stems flaccid or rigid, stem and branch tips long, tightly attenuate. Stem leaves extremely variable in form, closely or distantly spaced, erect, erect-spreading, or spreading, ovate, ovate-lanceolate, oblong-lanceolate, or lanceolate, 3--6 mm, firm or lax, concave throughout to flaccid, weakly concave or plane, acute to obtuse; margins erect or somewhat plane at base, erect-incurved or plane distally, erect-incurved or plane, serrulate or entire at apex; median cells 60--120 x 6--15 \um. Branch leaves similar to stem leaves except smaller, or closely spaced, erect to erect-spreading, narrowly lanceolate or linear-lanceolate, 2--3.5 mm, firm, concave to subtubular, long-acuminate; margins involute throughout, erect to involute, serrulate at apex. Perigonial leaves 0.8--1.1 mm. Perichaetial leaves 2.4--3.4 mm, oval to suborbicular, obtuse, usually lacerated across apex. Seta 0.1--0.2 mm. Capsule immersed to slightly emergent, subcylindric to cylindric, 2--2.5 mm; operculum conic, 1 mm; endostome trellis imperfect, cilia connected only in distal half in a lattice. Calyptra mitrate, 1.3--1.5 mm. Spores 16--18 \um, lightly papillose.

 

Rocks, roots, stumps, logs, in streams that are often seasonally dry; low to high elevations (2--1005 m); Greenland; Alta., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis.

 

Fontinalis sphagnifolia has long, tightly attenuate branch and stem tips and non-keeled leaves with often relatively short, long-rhomboidal median leaf cells. In all other features, however, it is remarkably variable. Typically the species is found in shallow streams and pools that are seasonally dry. The regular seasonal alternation between aquatic and terrestrial environments produces plants with two distinctly different leaf forms. Leaves formed after a prolonged dry period (vernalis-expression) or in sluggish water are medium-sized, loosely flaccid, ovate-lanceolate, plane to weakly concave, and have plane or erect to incurved apical margins. Leaves formed late in the aquatic period (aestivalis-expression) or in faster-moving streams are smaller in size, stiff, linear-lanceolate, strongly concave and have consistently erect to incurved apical margins. There are many collections that have a combination of vernalis-expression and aestivalis-expression leaves; whether or not this combination is the result of leaves formed during the transition from aquatic to terrestrial environments is unknown. Most of these intermediate collections fall within the lescurii-expression of F. sphagnifolia. The leaves in this expression are small and linear-lanceolate, but flaccid and have a mixture of plane and erect apical margins. When well developed the vernalis-expression of F. sphagnifolia has stem leaf apices with quadrate to short-rhomboidal leaf cells, and this has been erroneously considered an important feature of the species. Apical leaf cell shape within Fontinalis appears to be positively associated with leaf apex shape: the broader the leaf apex the shorter and broader the apical leaf cells.

Fontinalis novae-angliae, the duriaei-expression of F. hypnoides, and F. redfearnii are similar to the vernalis-expression of F. sphagnifolia in size and aspect. Fontinalis novae-angliae differs from the vernalis-expression of F. sphagnifolia in having short, often tumid branch and stem apices and firm leaves that are consistently concave with incurved to involute apical margins. The duriaei-expression of F. hypnoides is similar to the vernalis-expression of F. sphagnifolia in having weakly concave to plane leaves; it differs in having leaves with consistently plane apical leaf margins and longer median leaf cells. Fontinalis redfearnii differs from F. sphagnifolia (vernalis-expression) in having loosely foliate stem tips.

Fontinalis dalecarlica has been confused with the aestivalis-expression of F. sphagnifolia because of similar size, long, slender, tightly attenuate branch and stem tips, and strongly concave leaves. Fontinalis dalecarlica differs in ovate-lanceolate to lanceolate rather than narrowly lanceolate or linear-lanceolate leaves that are flat with loosely reflexed margins when dry. In addition, the apical leaf margins in F. dalecarlica vary from plane to erect. Large expressions of F. sullivantii can be very similar in size and aspect to the lescurii-expression of F. sphagnifolia, but that species has consistently plane apical leaf margins. Although F. sphagnifolia has generally been unrecognized in eastern North America, it is one of the most common Fontinalis species in the region. Nearly all the synonyms placed here under F. sphagnifolia were previously put under F. novae-angliae.

 

9. Fontinalis sullivantii Lindberg, Oefvers. Förh Finska Vetensk.-Soc.. 12: 77. 1869 [1870]

 

Fontinalis disticha Hooker & Wilson in Drummond; F. disticha Hooker & Wilson var. tenuior Sullivant; F. lescurii Sullivant var. gracilescens Sullivant; F. dichelymoides Lindberg; F. filiformis Sullivant & Lesquereux in Austin; F. flaccida Renauld & Cardot; F. renauldii Cardot; F. langloisii Cardot; F. filiformis var. tenuifolia Cardot; F. missourica Cardot; F. microdonta Renauld ex Cardot

 

Plants slender to medium-sized, to 25 cm, dark green, green, yellowish green, or pale green. Axillary hairs 480--600 \um, 6--10 cells, basal cell red, quadrate, distal cells hyaline or reddish, long-cylindric. Stems rigid or flaccid; stem and branch tips short or long attenuate. Stem and branch leaves dimorphic, differing greatly in size. Stem leaves narrowly lanceolate to linear, 2--6(--9) mm, widely spaced, erect-spreading to spreading, flaccid or firm, subconcave at base, plane, concave, or tubular above; apices acuminate, acute to subobtuse; margins plane at apex, entire proximally, entire to serrulate at apex; median cells 80--150 x 4--8 \um. Branch leaves 2--4 mm. Perigonial leaves 1.0--1.2 mm. Perichaetial leaves 2--3 mm, oval to suborbicular, obtuse, usually lacerated across apex. Seta 0.25--0.30 mm. Capsule immersed to slightly emergent narrowly cylindric, 1.7--2.5 mm; operculum conic, 0.8--1 mm; endostome trellis imperfect. 12--20 \um. Calyptra mitrate, 1.0--1.3 mm. Spores 12--20 \um, lightly papillose.

 

Rocks, roots, tree bases, logs, sticks, and twigs, in streams, sloughs, swamps, or pools; low to medium elevations (0--580 m.); N.S.; Ala., Ark., Conn., Del., Fla, Ga., Ill., Ky., La., Maine, Md., Mass., Miss., Mo., N.J., N.H., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Va.; n Europe.

 

Fontinalis sullivantii is separated from other members of Fontinalis by its typically slender size and narrowly lanceolate to linear-lanceolate, strongly dimorphic branch and stem leaves that have consistently plane apical margins. Plants growing in pools or slow-moving streams have flaccid stems and limp, plane leaves. Those found in fast-moving streams have rigid stems and stiff, subtubular branch leaves. In addition plants of F. sullivantii can vary considerably in branching pattern (regular or sparse) and stem leaf length (4 or more versus 3 or less mm). Fontinalis sullivantii has four major expressions (see Allen 1991) that have somewhat discrete ranges. Recognizing them at the species level is unwarranted because of the many intermediate morphology collections that link the expressions together.

Three other slender species of Fontinalis with variously plane or concave leaves can be confused with F. sullivantii: F. dalecarlica, F. welchiana, and F. sphagnifolia (aestivalis-expression). Fontinalis dalecarlica resembles rigid forms of F. sullivantii, but it has monomorphic leaves that are strongly concave when wet, and flattened when dry with narrowly reflexed margins. Fontinalis welchiana and the aestivalis-expression of F. sphagnifolia often have weakly dimorphic leaves, and they can have the same flaccid aspect as F. sullivantii. They differ from F. sullivantii in having strongly concave branch leaves with erect to incurved apical margins. Dichelyma capillaceum is superficially similar to F. sullivantii in its slender aspect, widely spaced branches, and long, narrow leaves. It differs from F. sullivantii in having keeled leaves with long, single costae.

Fontinalis redfearnii is the only other Fontinalis species with strongly dimorphic leaves. It differs from most collections of F. sullivantii in its much larger size and stiffer stems, but there are robust, stiff forms of F. sullivantii that closely approach F. redfearnii in size. Fontinalis redfearnii, however, differ from all forms of F. sullivantii in having broadly obtuse stem leaf apices.

 

10. Fontinalis welchiana B. H. Allen, Brittonia 40: 181. 1988

 

Plants slender, to 20 cm, green, yellow-green, or reddish yellow. Axillary hairs 450--530 \um, 5--10 cells, basal cells red, quadrate, distal cells hyaline or reddish, long-cylindric. Stems stiff; stem and branch tips shortly attenuate. Leaves weakly dimorphic or monomorphic. Stem leaves oblong-lanceolate, 2.5--4 mm, erect wet, erect-spreading dry, moderately concave; apices acute to obtuse, serrulate or entire; margins erect to incurved at apex; median cells 50--80 x 5--8 \um. Branch leaves ovate-lanceolate to lanceolate, 1.5--2 mm, strongly concave; apices acute, serrulate; margins incurved at apex; median cells 40--65 x 7 \um. Perigonial leaves 0.7--0.8 mm. Perichaetial leaves 2.6--3 mm, ovate to suboval, broadly rounded, often lacerated across apex. Seta 0.2 mm. Capsule emergent, cylindric to subcylindric, 2--3 mm; operculum conic, 0.5 mm; endostome trellis nearly perfect, latticed ½--3/4 their length. Calyptra mitrate, 1.5 mm. Spores 20--40 \um.

 

Rocks, ledges, and roots, in streams or seasonally dry pools, also constantly submerged in rivers and spring runs; low to medium elevations (152--580 m); Ark., Ill., Mo., Okla.

 

Fontinalis welchiana is a slender species of shallow streams that are seasonally dry; but also permanently submerged in rivers or deep spring runs. Plants from the two habitats have distinctly different aspects. Those exposed to seasonal drying have a soft aspect with weakly dimorphic leaves that are often plane to subconcave below when dry. Plants that are permanently submerged are stiff with monomorphic, long-lanceolate leaves that are strongly concave wet or dry. Both forms have smoothly imbricate to attenuate branch and stem tips, and leaves with erect to incurved apical margins.

Fontinalis sullivantii, F. sphagnifolia (aestivalis-expression), and F. dalecarlica are slender species with variably plane or concave leaves that can be confused with F. welchiana. In aspect, stiff forms of F. sullivantii are especially difficult to distinguish from the permanently submerged expression of F. welchiana. But F. sullivantii lacks attenuate branch and stem tips, and has strongly dimorphic leaves with plane apical margins. Both forms of F. welchiana can be confused with F. sphagnifolia (aestivalis-expression) and F. dalecarlica because they all have attenuate branch and stem tips and concave leaves that when dry can have erect to incurved apical leaf margins. Fontinalis sphagnifolia (aestivalis expression) differs in having very long-attenuate branch and stem tips, and lanceolate to linear-lanceolate branch leaves. Fontinalis dalecarlica and F. welchiana are remarkably alike in aspect and branch leaf form; F. dalecarlica differs in having monomorphic leaves that when wet have plane or erect to incurved apical margins, and when dry are usually flattened with narrowly reflexed margins. Fontinalis dalecarlica also differ from F. welchiana in having immersed, ellipsoid to oval capsules, and acute or apiculate perichaetial leaves.