Monographs Details: Asterella
Bischler, Hélène, et al. 2005. Marchantiidae. Fl. Neotrop. Monogr. 97: 1--262. (Published by NYBG Press
Synonyms:Fimbraria Nees, Fimbriaria Steud., Hypenantron, Marchantia tenella L., Asterella tenella (L.) P.Beauv.
Description:Genus Description - Thallus prostrate, sometimes with pungent "fishy" smell, green, often purplish pigmented especially beneath, thin and delicate or thick and leathery. Branching of terminal apical adventitious branches, terminal branches or stipitate-based ventral branches. Epidermal pores slightly elevated, simple, with 4-8 radial rows of cells in concentric rings, radial walls of cells sometimes somewhat thickened but not stellate. Assimilatory tissue of 1 to several layers of overlapping air chambers that are empty or subdivided by secondary walls. Ventral tissue often mycorrhizal; oil cells scattered. Rhizoids smooth and pegged. Ventral scales in 2 rows on midrib, colorless or violet to purplish pigmented, asymmetrical, with 1 or 2 lanceolate to ovate appendages often somewhat constricted at base, with scattered oil cells in body and sometimes in appendage, margin with few to many slime-papillae. Asexual reproduction by specialized propagules lacking, but sometimes with tuberous persistent branch tips. Monoecious or dioecious. Antheridia scattered or in cushions on main thallus or main or reduced branches. Archegonia in cushions bounded by scales, 2-4 per archegonial cavity, terminal on main thallus or on large or reduced ventral branches. Archegoniophore stalk elongating after fertilization, with or without air chambers, with a single rhizoid furrow, with or without scales at top and bottom. Receptacle of mature archegoniophore subglobose when young, becoming conical, ovoid or inversely saucer-shaped when mature, 2- to 6-lobed, with compound pores. Involucres flaplike, usually hidden beneath lobes; involucres opening obliquely downwards. Calyptrae 3-to 4-layered. Sporophytes 1 per involucre, with bulbous foot and scarcely elongating seta, enclosed by a colorless or pigmented pseudoperianth consisting of a unistratose basal cup and 5-18 lanceolate lobes attached at apex when young, remaining attached or becoming free at maturity. Capsules globose, dehiscing when ripe in upper 1/3-1/4 as an irregular or regular, discoid cap, wall without thickenings. Spore/elater ratio 4:1. Elaters with 1-3 helical bands. Spores 2000-4000 per capsule, 55-150 µm diam., yellow, orange, brown, or black, proximal and distal surfaces with similar or dissimilar sculpturing, areolate, alveolate, or ridged, sometimes with equatorial pores, trilete mark distinct. Gametophytic chromosome number mostly n = 9.
Discussion:A genus of 80-90 species with an almost cosmopolitan distribution from the tropics to the Arctic, but with most species in temperate zones, especially in the mountains of Europe, Asia, and America. In the New World 18 species are accepted, of which 8 occur in N America and 11 in C and S America; only 1 species, A. echinella, occurs in both N and C America, and 1, A. chilensis (Nees & Mont.) A. Evans is found only in S South America outside the Flora Neotropica area. Five species have rather wide distributions in tropical America, A. dominicensis S. Am., A. venosa (Lehm. & Lindenb.) A. Evans, A. macropoda (Spruce) A. Evans, A. elegans (Spreng.) Trevis., and A. lateralis M. Howe; the remainder are much more localized particularly in Mexico. None of the neo-tropical species occurs in other continents; most are found in mountainous regions except A. venosa (Lehm. & Lindenb.) A. Evans, A. elegans (Spreng.) Trevis., and A. echinella (Gottsche) Underw., which occur in the tropical lowlands. Some species are xeromorphic and drought-tolerant; others are hygromorphic and drought-intolerant. The xeromorphic species have inrolling thallus margins, whereas the hygromorphic species sometimes perennate by persistent tuberous thallus tips. Asterella species mostly grow on soil or rock, rarely on humus and never on wood. Many are weedy and colonize road cuttings and unstable habitats. Substrates may be acidic or calcareous. They are found in grasslands, savannahs, forests, often close to water; some are found on old lava flows. In the tropics they are rare in lowland forests but frequent in the temperate and alpine zones, from sea level up to 4000 m. Carpocephala and sporophytes are commonly produced; gemmae are absent.