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12. OXYMITRACEAE Müller Frib. ex Grolle
Alan
T. Whittemore
Plants thallose, 6--13 x
1.8--3 mm, branching dichotomous; thallus dorsal surface with a narrow
[broad] median groove; dorsal pores simple, cells surrounding pores with
radial walls strongly thickened; air chambers much higher than broad, without
green filaments. Ventral scales irregularly scattered over thallus, tapering to
slender apices that function as appendages but are not clearly set off from
body of scale. Brood bodies absent. Antheridia embedded in dorsal tissue
of thallus. Sporophytes embedded in thallus beneath pyramidal involucres,
indehiscent, spores liberated by disintegration of wall and surrounding
gametophytic tissues; foot rudimentary, seta absent; sterile cells in spore
mass thin walled, usually disintegrating before capsule matures.
Genus
1, species 2 (1 genus and 1 species in the flora): North America, South America, Mediterranean
basin, South Africa.
1. OXYMITRA Bischoff ex Lindenberg, Nova Acta
Phys.-Med. Acad. Caes. Leop.-Carol.
Nat. Cur. 14 (suppl.): 124. 1829 *
[Greek oxy, sharp, and mitra,
miter, alluding to pyramidal involucres]
Thallus with a sharp,
narrow median groove. Ventral scales conspicuous,
triangular, tapering gradually into a slenderly
attenuate apex. Antheridia in linear receptacles in median groove of
thallus. Sporophytes enclosed in involucres that are crowded in median
groove of thallus. Spores black and opaque, angular.
Species
2 (1 species in the flora): North
America, South America, Europe, sw Asia, Atlantic
Islands, s Africa.
1. Oxymitra
incrassata (Brotero) Sérgio
& Sim-Sim, J. Bryol. 15: 662. 1989
Riccia incrassata Brotero, Fl. Lusit. 2: 428. 1804; Oxymitra paleacea Bischoff
Thalli densely cespitose, upper surface pale green or with brown
margins, underside dark brownish purple, 6--13 x 1.8--3 mm, simple or once dichotomous;
when dry inrolled or sharply infolded
along midline; areoles 0.06-0.1 mm across, not conspicuous, not subdivided,
regular in shape; pores bordered by 5--6 cells with radial walls strongly
thickened, otherwise hardly differentiated.
Ventral scales white from a
purple base, 1.7--2.3 x 0.4--1.4 mm, plane or margins inrolled
when dry, extending far beyond margin of thallus, when dry incurved and more
or less covering thallus. Sexual condition autoicous or
dioicous. Involucres separate, pyramidal or ovoid, purple, 1.3 x 0.6--1 mm,
in one row, seldom several irregular rows, in median groove of thallus; upper
part of involucre breaking away at maturity and carrying away the upper
capsule wall to expose the spore mass.
Spores (90--)118--175 \um, outer face regularly areolate.
Thin
soil over nonporous rock that is wet after rains and very dry during dry
spells; 75--750 m; Kans., Mo., Okla., Tex.; Mexico; South America; Europe; sw Asia; Atlantic Islands.
Variation in this species is discussed by R. L. McGregor (1955).
SELECTED REFERENCE McGregor, R. L. 1955.
Taxonomy and ecology of Kansas Hepaticae. Univ. Kansas Sci. Bull. 37: 55--141.
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