BFNA Title: Acrobolbus
XX. ACROBOLBACEAE E A. Hodgson
Laura Briscoe and John J. Engel
Plants prostrate to erect. Branches originating from the axils of lateral leaves [occasionally from axils of underleaves]; sometimes with flagellae. Rhizoids hyaline, tending to be in fascicles from ventral base of leaves, sometimes scattered. Leaves alternate, succubous, concave to somewhat convex, [unlobed] bilobed [or rarely 2--4(--5)-lobed], margins entire or bearing rhizoids [or dentate to dentate-ciliate]. Underleaves absent or vestigial [present and well developed]. Asexual reproduction lacking or by caducous leaves. Gynoecium terminal on leafy branches [or on abbreviated intercalary branches]. Subfloral inovations common. Perianth rudimentary or absent. Marsupium present, pendent.
Genera 6 (1 in flora): North America, Central America, South America, Europe, Asia, Africa, Atlantic Islands, Pacific Islands, Australia.
Acrobolbaceae is a small family, circumscribed in four subfamilies, with most of the diversity in the southern hemisphere. Acrobolbus, the sole North American member, belongs in the subfamily Acrobolboideae R.M. Schuster ex Briscoe. Plants of Acrobolboideae can grow terrestrially, as in A. ciliatus, or as epiphytes, but require very moist growing conditions. They often have a distinctive opaque quality in their leaves and, when fertile, develop large, hairy marsupia.
SELECTED REFERENCES: Schuster, R. M. 1980. Acrobolbus. In: The Hepaticae and Anthocerotae of North America east of the hundredth meridian. New York. Vol. 4, pp. 539--554. Schuster, R. M. 2001. Revisionary studies on austral Acrobolbaceae, I. J. Hattori Bot. Lab. 90: 97--116.
1. ACROBOLBUS Nees in C. M. Gottsche, J. B. W. Lindenberg & C. G. D. Nees, Syn. Hep. 5. 1844. [Greek: akros, at the tip, end, and bolbos, bulb, alluding to the apical marsupium]
Plants pure green to gray-, yellowish, whitish, or faintly bluish green to brownish. Branching in species that lack basal stolons sparing, the branches lateral-intercalary, [other species often with a system of basal stolons from which arise erect, leafy shoots that are mostly lateral-intercalary but at times ventral-intercalary in origin, the leafy branches also originating from sectors of the erect leafy shoots]; stoloniform axes absent, or (often) abundant, basal, all intercalary and often originating from basal sector of erect leafy shoots. Stems with cortical cells about equal in diameter to the medullary cells or smaller, the cortical cells thin-walled or slightly to strongly thick-walled and [in some species in 1--3(--4) layers]; medullary cells thin- to firm-walled. Rhizoids sometimes from margins of leaves, [or on stoloniform axes]. Leaves with insertion distinctly succubous throughout, [or succubous in dorsal half and subtransverse in ventral half]; the apex undivided to (often) retuse or bilobed to 0.3--0.6 the leaf length, the lobes frequently asymmetric and then with the dorsal lobe always smaller, the lobes acute [to acuminate or at times piliferous], entire, the lobes and lamina margins sometimes adorned with marginal rhizoids [or variously toothed]. Androecia lacking [terminal but becoming intercalary on leading shoots and then usually subfoliose, or on short lateral- or ventral-intercalary branches from lower leafless sector of shoot and then spicate; antheridia 1--3 to 5--10 per bract, the stalk long, to 29 cells long, 2--3-seriate]. Gynoecia (only juvenile known), terminal on leading shoots with a subfloral innovation when unfertilized [ or on short branches originating from basal stoloniform axes or from microphyllous sector of erect leafy shoots], bracts leaf-like, the outermost larger than leaves. Marsupium not seen [of Tylimanthus type, cylindrical or conical, the surface smooth or sparsely covered with rhizoids or with hyaline, stiff, unicellular hairs]. [Sporophyte with long seta, capsule ellipsoidal to long cylindrical with acute apex, the valves straight, not twisted, the wall 2--3 or more often 4--9-stratose, outer walls with nodular thickenings].
Species 40 (1 in the flora): North America, West Indies, Central America, South America, Europe, Asia, Africa, Atlantic Islands (including Macaronesia), Pacific Islands (including Hawaii and New Zealand), Australia.
SELECTED REFERENCES: Schuster, R. M. 1980. Acrobolbus. In: The Hepaticae and Anthocerotae of North America east of the hundredth meridian. New York. Vol. 4, pp. 539--554.
1. Acrobolbus ciliatus (Mitten) Schiffner in H.G.A. Engler & K. Prantl, Nat. Pflanzenfam.1 (3): 86. 1893
Gymnanthe ciliata Mitten, J. Proc. Linn. Soc., Bot. 5 (18): 100. 1861 (1860); Acrobolbus rhizophyllus Sharp; Acrobolbus (Lophocoleopsis) titibuensis (S. Hattori) S. Hattori; Leiocolea titibuensis S. Hattori; Lophozia curiossima Horikawa
Plants flexuous, prostrate, loosely creeping, opaque, greyish green to whitish yellow. the shoots 10--25(--35) x 1.5--2.2 mm. Stems slender, the cortical cells in surface view striate-papillose. Rhizoids often exceeding length of leaf. Lateral leaves strongly succubously inserted, plane to convex, subsymmetrical, ovate to ovate-quadrate to subquadrate-orbicular, often appearing subcuneate in situ, 2-lobed to 0.3--0.45, sporadic leaves exceptionally 2-lobed; lobes about equal in size, or commonly the ventral larger, the margins with several to many rhizoids developing with age (leaves towards shoot apices devoid of rhizoids), the rhizoids glistening, the lobe apices bluntly rounded or terminating in a single, often sharp, cell or in a rhizoid; sinus acutely angular to rounded at base; lamina margins edentate, armed with rhizoids similar to the lobes, the dorsal margin nearly straight to arched, the ventral margin typically more strongly arched than the dorsal; leaf cells with thin walls, trigones medium and straight-sided to large with sides slightly bulging; the median lamina cells (28--)32--38 x 25--32 \um in leaf middle, 32--40 x 24--28 \um at base; surface distinctly papillose. Oil bodies nearly occluding the cell lumen, large for cell size, somewhat opaque and greyish, (3--4)5--10(--12), finely granular, subspherical to ovoid to ellipsoid, 6 x 9 to 10 x 15 \um, or smaller in cells with 8 or more oil-bodies. Underleaves lacking, except at shoot apices, 1--2 cells wide at base, 2--3 cells long, bearing several slime papillae. Androecia lacking in flora area. Sporophyte unknown.
On damp to moist, usually shaded noncalcareous rocks, in areas with high atmospheric moisture or spray, such as near waterfalls or cascades; restricted to elevations around 600 m; Alaska (Aleutian Islands), Ga., N.C., S.C., Tenn.; Asia (Japan, Sikkim-Himalaya).
The only species of this family in North America, Acrobolbus ciliatus is locally rare and potentially threatened due to limited suitable habitat. It often occurs in only small quantity, and in admixture with other bryophytes. It is an oceanic species restricted to widely disjunct areas, the stations rare and local. Regionally, it is found in small areas of the southern terminus of the Appalachians, ranging from the upper edge of the Southern Escarpment into the Smoky Mountains. Appalachian populations are assumed to be sterile, with only immature female plants observed. Male plants of the species appear to be restricted to Himalayan and Japanese populations. The most striking feature of this species are the long rhizoids borne on leaf margins. The oil body information is from R. M. Schuster (1980).