Argyrochosma microphylla
Argyrochosma
small-leaf false cloak fern
false cloak fern
scales brown.
compact, erect to ascending, usually unbranched;
scales tan to brown, rarely black, concolored, subulate to narrowly lanceolate, margins entire.
7–25 cm.
monomorphic, clustered, 3–30 cm.
brown, 0.75–1.5 mm diam.
brown or black, rounded, flattened, or with single longitudinal groove adaxially, glabrous except for a few scales near base, with single vascular bundle.
deltate to ovate, 3–4-pinnate proximally, leathery, abaxially and adaxially glabrous;
rachis flattened or shallowly grooved adaxially.
lanceolate, ovate, or deltate, 2–6-pinnate, leathery to somewhat herbaceous, abaxially glabrous or covered by whitish farina, adaxially glabrous or sparsely glandular, dull, not striate;
rachis straight or flexuous.
articulate, dark color of stalks stopping abruptly at segment bases;
segment margins recurved to revolute, often concealing sporangia;
veins obscure adaxially.
of blade stalked or subsessile, usually free from costae, elliptic to ovate or deltate, usually less than 4 mm wide;
base often ± cordate, stalks lustrous and dark colored;
segment margins plane or often recurved and forming confluent, poorly defined false indusia extending entire length of segment.
of ultimate segments free, usually obscure, pinnately branched and divergent distally.
, when present, greenish, narrow, clearly marginal, occasionally concealing sporangia.
submarginal, borne on distal 1/3 of secondary veins, containing 64 spores.
scattered along veins on abaxial leaf surface, often submarginal, containing 64 or 32 spores, usually intermixed with farina-producing glands.
brown, tetrahedral-globose, with cristate or rugose surfaces, lacking prominent equatorial ridge.
glabrous.
costae straight to somewhat flexuous, branches rarely arising from prominent angles.
= 27.
= 54.
Argyrochosma microphylla
Argyrochosma
Argyrochosma microphylla is probably the most distinctive species of Argyrochosma in the flora. Chromosome studies by I. W. Knobloch et al. (1973) suggest that it may include diploid and tetraploid cytotypes.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The species of Argyrochosma traditionally have been assigned to either Notholaena or Pellaea. Comparative studies (M. D. Windham 1987) have revealed that members of Argyrochosma are not closely related to Notholaena as typified by N. trichomanoides (Linnaeus) Desvaux. The two genera show consistent differences in stem and leaf morphology, sporangial distribution, spore color and ornamentation, chromosome base number, gametophyte morphology, and chemical composition of the farina.
Argyrochosma is more closely related to Pellaea (M. D. Windham 1987) and members of these genera are occasionally confused. These two groups are easily distinguished, however, based on the presence or absence of farina, leaf segment size and shape, and characteristics of the stem scales and leaf margins. In addition, all species of Argyrochosma thus far examined have a chromosome number based on x = 27, unique among cheilanthoid ferns. These differences suggest that Argyrochosma is monophyletic and worthy of recognition as a distinct genus.
Species ca. 20 (6 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Abaxial surfaces of blades glabrous, lacking whitish farina. | → 2 |
1. Abaxial surfaces of blades obscured by whitish farina. | → 3 |
2. Ultimate leaf segments articulate, dark color of stalks stopping abruptly at segment bases; rachises flattened or shallowly grooved adaxially; margins of fertile ultimate segments usually revolute, often concealing mature sporangia. | A. microphylla |
2. Ultimate leaf segments not articulate, dark color of stalks continuing into segment bases abaxially; rachises rounded adaxially; margins of fertile ultimate segments plane to somewhat recurved, not concealing mature sporangia. | A. jonesii |
3. Ultimate leaf segments articulate, dark color of stalks stopping abruptly at segment bases; margins of ultimate segments plane, not recurved or revolute; sporangia following secondary veins for most of length. | A. incana |
3. Ultimate leaf segments not articulate, dark color of stalks continuing into segment bases abaxially; margins of ultimate segments usually recurved or revolute; sporangia following secondary veins for short distance near segment margin. | → 4 |
4. Pinna costae distinctly flexuous; branches arising from prominent angles. | A. fendleri |
4. Pinna costae straight or nearly so; branches not arising from prominent angles. | → 5 |
5. Petioles chestnut brown, 0.50–0.75 mm diam.; blades somewhat herbaceous; veins often visible adaxially; sporangia containing 64 spores. | A. dealbata |
5. Petioles reddish brown to black, usually more than 0.75 mm diam.; blades leathery; veins obscure; sporangia containing 32 spores. | A. limitanea |
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