Microsorum siamense Boonkerd
Microsorum siamense Boonkerd, Blumea 51: 143. 2006. – Type: Thailand, Yala, P.V. Fern 1 (holo L; iso BCU).
Rhizome 3.2–4.2 mm in diam., not white waxy, approximately cylindrical with scattered strands of sclerenchyma, vascular bundles in cylinder 9 or 10, sclerenchyma strands 60–240, roots densely set, bearing two rows of close to imbricate fronds. Scales densely set, slightly spreading, widest near the base, ovate or triangular, 3–3.5 by 1–1.3 mm, peltate, margin denticulate, apex acuminate to slightly caudate, clathrate throughout, dark black on central region. Phyllopodia more or less distinct, 3.1–4.1 mm apart. Fronds monomorphous (well proportioned to the rhizome diameter), subcoriaceous, iridescent blue-green in colour when living, Havana brown to raw umber in dry specimens. Laminae simple, hydathodes scattered on upper surface, elliptic to narrowly elliptic, 13–23.5 by 2.2–4.5 cm, index 4.5–5.9, base attenuate, the stipe more or less winged, margin entire undulate, apex acute to long acuminate, costa raised on lower surface, slightly raised on upper surface. Venation: connecting veins forming a row of about equally sized areoles between two adjacent veins and no prominent veinlet situated parallel to the veins; the venation is hidden in living specimen, free veinlets simple or 1 or 2 times forked. Sori separate, mostly irregularly scattered on a simple free vein or on 2 or 3 connective veins, usually occupying the upper half portion of the lamina, more or less round, superficial, 4 –14 per cm2, 0.7–1.6 mm in diam.; paraphyses absent; sporangium hyaline when young, turning yellowish brown when, mature, sporangium annulus 17–21-celled, indurated cells 11–14; spores concave-convex , brightly golden yellow, 35–38 by 50–55 micrometres.
Distribution in Thailand
Endemic to Thailand.
In rock crevices on moist limestone rocks in semi-shade at 100 m alt.
Proposed IUCN Conservation Assessment
Data Deficient (DD). The distribution of this species in the wild is rather vague and any threats to the population(s) are unknown.
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