Cycas tansachana K. D. Hill & S.-L. Yang (1999)
Hill.,K.D. 1999. The genus Cycas (Cycadaceaea) in Thailand. Brittonia 51(1):48-73.

Plant arborescent: stems erect or sometimes decumbent, occasionally branched, 2-5 m tall, 10-18 cm diam. At narrowest point, bark thick, hard, corky, with regular polygonal fracturing, grey. Leaves 24-60, deep green, semiglossy, 1-1.7 m long, with white tomentum shedding as leaf expands, moderately keeled, with 130-200 pinnae, opposing pinnae inserted at 90-140? on rachis, rachis frequently terminated by a spine 1-3 mm long. Petiole 30-45 cm long (20-30% of total leaf), glabrous, unarmed or spinescent for 0-30% of length. Basal pinnae not gradually reducing to spines, 8-16 cm long. Median pinnae glabrous, simple, strongly discolorous, 17-30 cm x 8-12.5 mm, inserted at 60-70? to rachis, decurrent for 3-5 mm, narrowed to 2.5-4 mm at base (to 25-45% of maximum width), 10-17 mm apart on rachis, section flat, margins slightly recurved; apex acute, not spinescent; midrib flat or slightly raised above, raised below. Tomentum loose and shed early. Cataphylls narrowly triangular, soft, 5-6 cm long. Persistent, with a thick floccose orange-brown indumentum. Microsporangiate cones narrowly ovoid, yellow, 25-35 cm long, 11-13 cm diam. Microsporophylls lamina firm, not dorsiventrally thickened, 33-45 x 12-15 mm, fertile zone 27-40 mm long, sterile apex 6-15 mm long, level, apical spine prominent, sharply up turned, 1-3 mm long Megasporophylls 20-22 cm long, yellow to brown tomentose; ovules 2-4, glabrous; lamina orbicular, 100-140 x 60-70 mm, deeply pectinate, with 40-60 soft lateral spine 18-25 x 1-1.5 mm; apical spine distinct from lateral spines, 30-50 mm long, 5-7 mm wide at base. Seeds flattened-ovoid, 45-50 x 35-40 mm; sarcotesta yellow, not pruinose, 4 mm thick; fibrous layer present; sclerotesta smooth; spongy layer absent.

Distinguishing features.-This species is similar to C. clivicola in many respects, differing in the larger and distinctly keeled leaves with stiffer, broader pinnae. And the larger male cones, megasporophylls, and seeds. The bark is also somewhat thicker and more corky, and the crown of orange wool around newly developed cataphylls is not seen in any other Thai species.

Distribution and habitat.-Only known from limestone outcrops near Saraburi, growing in full sun or part shade in crevices in bare rock.

Conservation status.-Apparently quite restricted in occurrence and under severe pressure from plant collectors and limestone mining operations, this species should be regarded as threatened. The appropriate IUCN Red List category would be “Lower Risk-near threatened” (IUCN, 1994).

Etymology.-Honouring Mr. Kampon Tansacha, proprietor of the Nong Nooch Tropical Garden.