BFNA Title: Reboulia
Aytoniaceae - Reboulia
XX. REBOULIA Raddi Opusc. Sci. Bologna 2: 357. 1818, orthography conserved "Rebouillia" * [For de Reboul, Italian botanist]
Marie L. Hicks
Plants in depressed mats, dichotomously branched with occasional apical or lateral adventitious branches of ventral origin; green to dull green with purplish margins, underside purple; dorsal surface firm, not areolate; with slightly elevated air pores. Thalli 10‑‑18 cells thick medially, gradually tapering to the margins, the interior tissue with few oil cells; air chambers simple, without photosynthetic filaments; dorsal epidermis without oil cells, epidermal cells with thin walls and distinct trigones, air pores surrounded by 3‑‑6 concentric rings of cells with thickened walls and trigones; ventral scales in 2 rows, purple, lunate, with scattered oil cells and few slime papillae along the margins; appendages purplish with decolorate apices, linear, hair‑like; rhizoids dense along ventral midline, smooth or with internal pegs. Specialized asexual reproduction absent. Sexual condition monoicous; androecia dorsal, sessile, distinct, discoid to reniform or lunate, thickened, purplish, ringed by small subulate purple scales; gynoecia terminal, in apical notch, gynoecial stalk with one rhizoid furrow and white hair‑like scales at base and apex; carpocephalum hemispheric, the proximal half lobed, each lobe with a 2-labiate slit, and containing one sporophyte; pseudoperianth absent. Sporophyte seta not elongating. Capsule spherical, irregularly circumscissile, the distal portion disintegrating; capsule wall without thickenings. Spores areolate, the areolae bordered by winglike ridges; elaters 2‑‑4 spiral.
Species 2 (1 in the flora): worldwide except Antarctica, on soil.
SELECTED REFERENCES Evans, A. M. 1923. Rebouliaceae. In C. C. Haynes, M. A. Howe and A. W. Evans. 1923. Sphaerocarpaceae--Marchantiales, Sphaerocarpaceae, Riellaceae, Ricciaceae, Corsiniaceae, Targioniaceae, Sauteriaceae, Rebouliaceae, Marchantiaceae. North American Flora Ser. I, Vol. 14(1). New York Botanical Garden, New York. Frye, T. C. and L. Clark. 1937. Hepaticae of North America. University of Washington Publ. in Biology, University of Washington, Seattle. Schuster, R. M. 1992. The Hepaticae and Anthocerotae of North America. Vol. 6. Field Museum of Natural History, Chicago.
The genus can be recognized by the conspicuous cluster of white hair‑like scales at both the base and apex of the gynoecial stalk and by the very narrow, hair‑like scale appendages.
1. Reboulia hemisphaerica (Linnaeus) Raddi Opusc. Sci. Bologna 2: 357
Marchantia hemisphaerica Linnaeus, Sp. Plant. 1138. 1753
Plants with somewhat crenulate, undulate margins. Thalli 2--4 × 0.5--0.9 cm, elongate, slightly widened distally; epidermis persistent, smooth; air pores and areolation indistinct; epidermal cells 45--50 × 30‑‑35 µm with small bulging trigones; air pores surrounded by 3‑‑5 concentric rings of 6‑‑8 cells each; ventral scales with decolorate margins and scattered oil cells; appendages 2‑‑3 per scale, linear and hair‑like, 2‑‑3 cells wide, ending in 1‑‑3 single cells. Sexual condition paroicous (rarely polyoicous, but usually with some paroicous thalli in the mat); androecia reniform to lunate or reduced and chevron-like, positioned 1‑‑10 mm posterior to the base of the gynoecial stalk; gynoecium in apical notch, stalk 1.5‑‑3 cm, purplish; carpocephalum green, with air pores in the upper portion, 4‑‑5 lobed below, each lobe directed downward, the slit widening to form a circular opening as the sporophyte expands. Sporophyte capsule pale greenish; Spores yellow, 65‑‑80 µm; elaters 250‑‑350 × 10‑‑12 µm, 2‑‑3 spiraled.
Capsules mature March--August. Soil over rock that is commonly but not exclusively calcareous, habitats that are at least periodically moist, temperate areas; subcosmopolitan: Alta, BC, Man., Ont, Que.; Ala., Ariz., Ark., Calif., Colo., Conn., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Oreg., Pa., R.I., S.C., Tenn., Tex., Utah, Va., Vt., W.Va., Wis.; South America; Europe; Asia; Africa; Australia; Pacific Islands.
Reboulia hemisphaerica, with its wide distributional range, exhibits considerable variation. From time to time these plants have been variously described as autoicous or dioicous as well as paroicous. The North American populations appear to be rather consistently paroicous, rarely failing to produce either androecia or gynoecia. When this failure occurs, some populations may appear to be autoicous or dioicous but paroicous individuals can usually be found within the mat of plants. Also, in Reboulia collections, the size of androecia decreases with age and, before elongation of the gynoecial stalk, androecia are quite turgid and bear marginal scales. As the gynoecial stalk elongates and sporophytes mature, the androecia shrink and marginal scales often fall away. Additional synonyms for the species are given by T. C. Frye and L. Clark (1937).
DOUBTFUL TAXA Reboulia hemisphaerica subsp. australis R. M. Schuster has been reported from Quebec, Massachusetts and Virginia. This name, based on New Zealand plants, is a synonym of R. queenslandica (Stephani) M. L. Hicks. The Australia and New Zealand populations are rather consistently autoicous, and no undoubted North American material has been located. For following two taxa, Reboulia hemisphaerica subsp. acrogyna (R. M. Schuster) R. M. Schuster (reported from Texas), R. hemisphaerica subsp. dioica R. M. Schuster (reported from North Carolina), material is not available, and the assigned characters do not justify taxonomic recognition.