Microsorum thailandicum Boonkerd & Noot.
Microsorum thailandicum Boonkerd & Noot., Blumea 46: 581. 2001.
Rhizome 4–5 mm diam., not white waxy, approximately cylindrical with scattered strands of sclerenchyma, vascular bundles in cylinder 8–12, the sclerenchyma strands 40–240, roots densely set. Scales densely set, slightly spreading, widest near the base, ovate or triangular, 2.5–4.5 by 0.6–1.4 mm, pseudopeltate but the lobes often connivent or some scales peltate, the margin denticulate, apex acuminate to slightly caudate, clathrate throughout, dark black on central region. Phyllopodia more or less distinct, 1.6–3.6 mm apart. Fronds monomorphous (well proportioned to the rhizome diameter), subcoriaceous, iridescent blue in colour when living, linoleum brown in dry specimens. Laminae simple, narrowly elliptic, 15–35 cm long, 1.2–2.1 cm broad, index 7–12, apex long acuminate, base attenuate, the stipe more or less winged, margin entire, costa raised on lower surface, grooved on upper surface. Venation: the first connecting vein forming one row of relatively small, primary costal areoles parallel to the costa, other, larger, areoles in a row between two veins; the venation is hidden in living specimen, free veinlets simple or once or twice forked. Sori separate, mostly irregularly scattered on simple free or on 2 or 3 connective veins, usually occupying the apical half of the lamina, more or less round, slightly immersed, 4–20 per square cm, 0.6–2 mm diam.; paraphyses absent; sporangium hyaline when young, turning black when mature, sporangium annulus 26–31-celled, indurated cells 14–21; the spores concave-convex, yellowish hyaline , 61–76 by 44–59 micrometres.
Distribution in Thailand
Endemic to Thailand.
Rock crevices on rather dry rock of limestone hill in semi-shade, 250–300 m alt.
Proposed IUCN Conservation Assessment
Endangered EN B1ab(iii)(v). It was noted in the protologue that this plant first came to the authors' attention from plants in the Sunday market in Bangkok. In the wild it is only known from limestone habitats in Chumphon Province. The conservation assessment given is a precautionary one as not enough is known about the effect that the harvesting for trade is having on the populations, nor indeed what its exact distribution is. With further research it could be that a higher threat category is needed.
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