Etymology: From the Latin pinna, first division of a compound leaf, with the compound prefix simplici-, simple, referring to the simple leaflets in contrast to the divided leaflets of C. micholitzii, of which this taxon was initially regarded as a variety. Literature: Smitinand 1972. Illustrations: Smitinand 1971, Wang 1996. Historical notes: Described in 1971 as a variety of C. micholitzii by Danish botanist Tem Smitinand, raised to species rank in 1996 by Australian botanist Ken Hill. Suvatabandhu (1961) had misapplied the name C. immersa to this taxon. Distinguishing features: The almost totally subterranean habit with the very sparse crown of large, erect leaves with few, broad and well-spaced leaflets immediately distinguish this species from all other Thai cycads. The almost totally subterranean habit with the very sparse crown of large, erect leaves with few, broad and well-spaced leaflets, small microsporangiate cones, small megasporophylls with short spines on the apical lamina and small seeds distinguish this species within the group of acaulescent species occurring in the Indochina region (section Stangerioides). Allies of C. simplicipinna include the strikingly distinctive C. micholitzii and C. multipinnata of southern China and Vietnam, and C. simplicipinna is in fact an outlier of this predominantly Chinese and Vietnamese group of species. Distribution and habitat: Widely distributed in the mountains in the north of Thailand, only above about 600 metres elevation, usually in wetter and more sheltered sites in deep shade in tall closed evergreen forests. This species also occurs in northern Burma, Laos and Vietnam. Individuals are usually scattered and sporadic in occurrence, and dense stands are uncommon. Conservation status: A very widespread species, but usually not occurring in large or dense populations. Although its habitat is continually being reduced, many populations remain across this range, with a number in conservation areas, and it is not under any immediate threat of extinction. IUCN (1994) status LR, cd. Description:
Stems acaulescent, 8-14 cm diam. at narrowest point; 2-5 leaves in crown. Leaves bright green to deep green, highly glossy, 90-250 cm long, flat (not keeled) in section (opposing leaflets inserted at 160-180° on rachis), with 35-90 leaflets, with orange tomentum shedding as leaf expands; rachis consistently terminated by paired leaflets. Petiole 35-140 cm long (40-60% of total leaf), petiole glabrous, spinescent for 60-100% of length. Basal leaflets not gradually reducing to spines, 120-300 mm long. Median leaflets simple, strongly discolorous, 200-600 mm long, 14-20 mm wide, inserted at 50-65° to rachis, decurrent for 5-10 mm, narrowed to 2.5-4 mm at base (to 15-30% of maximum width), 20-40 mm apart on rachis; median leaflets section flat; margins flat or undulate; apex softly acuminate, not spinescent; midrib raised above, flat below. Cataphylls narrowly triangular, soft, pilose, 40-50 mm long, articulated. Pollen cones fusiform, cream, 15-21 cm long, 2.2-4 cm diam.; microsporophyll lamina soft, not dorsiventrally thickened, 12-14 mm long, 7.5-10 mm wide, fertile zone 8-10 mm long, sterile apex 3-6 mm long, raised, apical spine absent. Megasporophylls 7-12 cm long, brown-tomentose; ovules 2, glabrous; lamina ovate, 45-55 mm long, 18-35 mm wide, deeply pectinate, with 10-14 soft lateral spines 15-25 mm long, 1.5-2 mm wide, apical spine not distinct from lateral spines. Seeds ovoid, 25-27 mm long, 18-21 mm wide; sarcotesta yellow, not pruinose; fibrous layer absent; sclerotesta verrucose. Spongy endocarp absent.
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