Medium-sized to rather large, terrestrial or often epilithic ferns with rather long-creeping stem clothed with dark, very long-tapering, non-clathrate bristles resembling scales in dried material; stele a radial solenostele. Petioles remote, weakly two-ranked, non-articulate, with one U-shaped vascular bundle or at the base with several strands arranged in a U (depending on the species), if one, the “U” bifurcating upward; petiole externally subterete or adaxially concave. Lamina at least once cleft dividing it into two (sub)equal parts (in most species again one to several clefts), the primary divisions anadromously divided, acroscopically more strongly developed, in living plants at the base twisted through 90°, in pressed specimens through 180°, their abaxial surface then facing upward; lamina hypostomatic with paracytic stomata, bristly with pale trichomes when young, glabrescent to glabrous when mature. Larger veins slightly unequally dichotomous, the larger branch facing outward; smaller veins forming a dense network with many free included veinlets (Fig. 44), abaxially prominent. Sori small, round, exindusiate, compital, scattered over the surface, or in narrow-lobed species irregularly few-seriate. Sporangia intermingled with hair-like soral trichomes with swollen top cell, small, several per sorus, maturing simultaneously or not, with short, 4-seriate stalk; annulus longitudinal, slightly oblique, almost entirely indurated, the stomium ill-defined from the bow. Spores monolete, ellipsoidal, achlorophyllous, 64 or fewer per sporangium; perispore thin; surface smooth or sometimes rugulose.
KeywordsClathrate Dian Venezuela Maxon Alphen
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