keys to the vascular plants of east texas - Botanical Research ...

368 PTERIDACEAE/ADIANTUM
7. Leaf blades usually tomentose abaxially OR if glabrous then the most distal
ultimate segments of leaf blades not cordate at base and � sessile (attached at
least partially by blade tissue) _________________________________________ Cheilanthes
ADIANTUM L. MAIDENHAIR FERN
AA genus of 150–200 species, nearly worldwide in distribution except at higher latitudes (�
60°), but most common in Andean South America (Paris 1993). It is sometimes placed in the
Adiantaceae. Some species are used medicinally and a number are cultivated as ornamentals
for their delicate, beautiful foliage. The position of the sporangia is definitive for identification—
in other related ferns with false indusia (e.g., Cheilanthes, Pellaea), the sporangia are borne on
the blade tissue beneath the false indusium, rather than on the false indusium itself as in Adiantum.
The leaves “have the unusual property that, when wetted, water beads-up into silvery
droplets that quickly roll off” (Hoshizaki & Moran 2001)—hence the scientific name. (Greek:
adiantos, unwetted, for the glabrous leaves, which shed raindrops)
REFERENCES: Fernald 1950b; Paris 1993.
Adiantum capillus-veneris L., (Venus’ hair), VENUS’-HAIR FERN, SOUTHERN MAIDENHAIR,
CULANTRILLO, MATTRESS FERN. Terrestrial or on rocks; stems (rhizomes) short-creeping; leaves �
monomorphic, weakly deciduous, closely spaced, numerous, lax-arching or pendulous, 15–75
cm tall; leaf blades 2(–more) pinnate, glabrous, membranous to thin-herbaceous, bright green,
the ultimate segments (= smallest subdivisions) usually wedge or fan-shaped to irregularly
rhombic (= 4-sided, diamond-shaped), ca. as long as broad, stalked; apical leaf margins recurved
to form false indusia; veins of ultimate leaf segments prominent, dichotomously
branched (= equally 2-forked), essentially parallel near the margins, a distinct midvein absent;
sporangia submarginal, borne on the abaxial (= beneath) surface of the false indusia. Continuously
moist calcareous areas, particularly limestone bluffs, rocks and ledges along streams.
Hays, Harris (BRIT), Bell, Bexar, Travis (BAYLU), Newton (TAES), Comal, Dallas, Kaufman, Hill,
McLennan, Orange, Washington, and Williamson (Turner et al. 2003) cos.; scattered nearly
throughout TX, common in some areas such as the Edwards Plateau; s 1/2 of U.S. from VA s to
FL w to CA, also SD and B.C. Sporulating May–Jan. The species has long been used medicinally
for conditions of the skin, scalp, and internal organs (Cheatham & Johnston 1995). Hoshizaki
and Moran (2001) considered this species, widespread in warm-temperate to subtropical areas,
to be one of the most widely distributed ferns in the world.
ARGYROCHOSMA (J. Smith) Windham FALSE CLOAK FERN
Plants usually on rocks; stems compact, erect to ascending; leaves monomorphic, clustered, to
only 25 cm long; petioles, rachises, and stalks of ultimate leaf segments dark brown, lustrous; leaf
blades 3–5 pinnate, deltate to ovate, the abaxial surfaces glabrous or covered by a whitish, mealy,
powdery material (= farina); ultimate leaf segments (= smallest subdivisions of leaf) small (� 4
mm wide), their margins recurved to revolute, forming false indusia, these often concealing or
partially concealing the sporangia; sporangia on the abaxial leaf surfaces, submarginal.
AA New World genus of ca. 20 species (Windham 1993b). While the species have been variously
treated in a variety of genera (e.g., Cheilanthes, Notholaena, and Pellaea), Windham
(1987b) segregated A. dealbata, A. microphylla, and related species as the genus Argyrochosma.
Morphological and chromosome evidence (x = 27—unique among cheilanthoid ferns) supports
its separate recognition (Windham 1993b), as does more recent molecular evidence (Gastony &
Rollo 1998). (Greek: argyros, silver, and chosma, powder, referring to whitish farina covering the
abaxial surface of leaf blades in most species)
REFERENCES: Tryon 1956; Windham 1987b, 1993b.