Trichomanes boschianum
Trichomanes petersii
Appalachian bristle fern, Appalachian filmy fern
dwarf bristle fern, Peters' bristle fern
long-creeping, slender, bearing widely spaced leaves;
stems covered with dark multicellular hairs of 2 kinds, unbranched gland-tipped hairs and branched or unbranched rhizoidlike hairs, sparsely rooted.
long-creeping, threadlike, and intertwining, bearing scattered leaves, covered with dark hairs of 2 types, 2-celled glandular hairs and elongate rhizoidlike hairs;
roots absent.
composed of short filaments of undifferentiated cells.
composed of short filaments of undifferentiated cells.
lanceolate, 1–2-pinnate-pinnatifid, 4–20 × 1–4 cm, bearing scattered short, unbranched, glandular hairs on principal veins;
petioles shorter than blades.
elliptic to oblanceolate, simple, 0.5–2 cm × 2–5 mm, ± entire, bearing simple or 2-cleft dark hairs on margin and 2-celled glandular hairs on petioles and veins;
petioles nearly as long as blades.
composed entirely of branching filaments.
composed entirely of branched filaments.
pinnate, without unconnected false veins.
weakly pinnate with numerous unconnected false veins.
involucres terminal on lateral veins at base of lobes, conic, not flaring at mouth;
involucral lips not dark-edged.
involucres usually 1 per leaf, terminal on blades, short-conic, flaring widely at mouth;
involucre lips not dark edged.
= 72, 108, 144.
= ca. 102.
Trichomanes boschianum
Trichomanes petersii
Although earlier treated as synonymous with the tropical American Trichomanes radicans Swartz, recent authors have agreed that Trichomanes boschianum is a distinct taxon endemic to eastern North America. It exists as fertile diploids and tetraploids with occasional sterile triploids. Diploid cytotypes are prevalent in western localities, and polyploids are more common to the east. Although occurring in climatically moderated habitats, most populations suffer heavy mortality from sporadic droughts. The plants are very slow to regrow, and many populations are currently but a fraction of their size of 20 years ago. They seldom show evidence of sexual reproduction although gametophyte colonies of this species may be found in the vicinity of fertile sporophytes. Identity of these gametophytes has been confirmed by enzyme electrophoresis, but most occurrences of independent Trichomanes gametophytes in the eastern United States have been shown by this method to be those of T. intricatum (D. R. Farrar 1985).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Trichomanes petersii has irregular meiosis and generally misshapen spores, but it produces some large and viable spores, presumably unreduced in chromosome number. Gametophytes, identified as this taxon by enzyme electrophoresis, have been observed to produce apogamous sporophytes. Therefore, the species seems capable of some reproduction by an apogamous life cycle. Sporophytes also reproduce vegetatively by dispersible buds formed on the leaves. Although some gametophytes in the vicinity of sporophytes have been shown to be Trichomanes petersii, most of the independent Trichomanes gametophyte populations of the eastern United States are T. intricatum.
Sporophytes of Trichomanes petersii and other species of subg. Didymoglossum form dense mats of imbricated leaves, often excluding all other vegetation. In this habit, as well as in their reduced size and absence of roots, they have adopted a growth form mimicking and successfully competing with bryophytes. In Louisiana and Mississippi, T. petersii occurs on trunks of Fagus and Magnolia. Elsewhere it is on noncalcareous rocks, but in Florida, T. petersii also occurs on chert boulders in limestone sinks and cliffs.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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