Historical notes: Although first collected in 1926, this singular and distinctive species was not recognised as new until the 1990's, and was undescribed until 1999. Distinguishing features: Although this species is similar in pollen and seed cones to the true C. circinalis from India, both molecular and morphological analysis place its affinities with the unusual C. lindstromii from Vietnam, and also indicate that these two species are allied to the C. pectinata group rather than the C. circinalis group. It distinguished from all other species in the region by the short leaves with few, coriaceous, short and broad leaflets and short, spine-free petioles, the small pollen cones with stout spreading spines on microsporophylls and the open seed cones with long megasporophylls and short spines on megasporophyll apices. Distribution and habitat: Known only from limestone outcrops of Khao Sam Roi Yot. This species grows in dense thickets in crevices jagged limestone outcrops with scant or no soil. Conservation status: Since it is known from a single locality only, this species should be regarded as a threatened species. IUCN (1994) Red List status VU D2.
Description:
Stems arborescent, to 1(-3) m tall, 8-10 cm diam. at narrowest point; 10-25 leaves in crown. Leaves bright green, highly glossy, 65-120 cm long, slightly keeled (opposing leaflets inserted at 120-140° on rachis), with 65-105 leaflets, with brown tomentum shedding as leaf expands; rachis frequently terminated by a spine 0-3 mm long. Petiole 8-30 cm long (10-30% of total leaf), petiole glabrous, unarmed (rarely with a few distal spines). Basal leaflets not gradually reducing to spines, 50-190 mm long. Median leaflets simple, strongly discolorous, 140-240 mm long, 8.5-13.5 mm wide, inserted at 45-60° to rachis, decurrent for 3-6 mm, narrowed to 2-4 mm at base (to 15-25% of maximum width), 10-20 mm apart on rachis; median leaflets section flat; margins flat; apex acute, not spinescent; midrib raised above, raised below. Cataphylls narrowly triangular, soft, thinly sericeous or lacking tomentum, 25-50 mm long, articulated. Pollen cones ovoid, yellow or orange, 20-25 cm long, 8-10 cm diam.; microsporophyll lamina firm, dorsiventrally thickened, 30-40 mm long, 12-18 mm wide, fertile zone 20-24 mm long, sterile apex 18-20 mm long, raised, apical spine prominent, gradually raised, 5-15 mm long. Megasporophylls 17-24 cm long, grey-tomentose; ovules 2-4, glabrous; lamina lanceolate, 60-90 mm long, 12-27 mm wide, shallowly pectinate or regularly dentate, with 14-24 pungent lateral spines 2-3 mm long, 1-1.5 mm wide, apical spine distinct from lateral spines, 24-40 mm long, 4-5 mm wide at base. Seeds ovoid, 35-40 mm long, 29-32 mm wide; sarcotesta orange, not pruinose, 1-2 mm thick; fibrous layer present; sclerotesta smooth. Spongy endocarp absent.
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