Photo Ken Hill
The Cycad Pages
Cycas siamensis

Cycas siamensis Miq., "Bot. Zeitung, Berlin 21: 334" (1863).
"TYPE: Thailand, Kanchanaburi, ""Siam, prope Kan-Boeric in collibus lapidosis"" m. Martii 1862, J. E. Teysmann s.n., Mar. 1862 (holo U, 2 sheets)."

Photo Ken Hill
Etymology: From the occurrence in Thailand, known as the Kingdom of Siam when this species was described.

Literature: Kurz 1877, Leandri 1931, (and as C. immersa), Ho & Duong 1960, Raizada & Sahni 1960, Suvatabandhu 1961 (and as C. immersa), Smitinand 1971, Smitinand 1972, Wang 1996, Tang et al. 1997, Hill & Yang 1999.

Illustrations: Schuster 1932, Smitinand 1971, Wang 1996

Historical notes: Described in 1863 by Dutch botanist Miquel. The name C. siamensis has been widely misapplied to C. clivicola in southern Thailand and Malaysia, and was misapplied to C. balansae in southern China (Cheng, Fu & Cheng 1975).

Distinguishing features: C. siamensis is distinguished by the flat leaves with a very short petiole and basal leaflets gradually reducing in size towards the spines. Megasporophylls are reminiscent of those of the C. pectinata complex, although smaller in all respects. They also differ in being usually densely brown-tomentose, with the tomentum persisting around their bases and on the trunk around the persistent leaf-bases. Male cones are smaller than those of the C. pectinata complex, and of a distinct oblong shape. The short-stemmed habit is also distinctive, plants reaching reproductive maturity before any aerial stem is developed. Another distinctive characteristic of C. siamensis is the sharply demarcated bulbous base, often becoming broad and plate-like in older individuals. Seeds show limited and apparently variable development of fibrous layer within the sarcotesta.

Plants vary in colour from white through yellow, orange to brown, depending on the colour of the hairs on the leaves. Variation may occur in one stand (Tak), or stands may be wholly white (Ban Sai Yok) or orange (Thung Luang). There are no other clear distinguishing features, and they must all be regarded as the same species.

Distribution and habitat: abundant in many places in central Thailand, and in Vietnam in the central plateau region from Buon Ma Thuot to Pleiku (Dac Lac and Kon Tum), with a disjunct occurrence in Thanh Hoa and Nghe An provinces in the north. Also recorded from Cambodia and Myanmar. This species occurs in full sun to light shade in low open woodland on flat country or on low hills, often in dense stands. Host woodland is often dominated by Dipterocarpus tuberculatus with a wide range of associated trees such as Erythrina and Bombax. These woodlands are characteristically seasonally wet and dry with the monsoon weather patterns of the region, with particularly pronounced and extended dry periods.

Conservation status: A widespread and locally extremely abundant species. Although its habitat is continually being reduced, large populations remain, and it is not under any immediate threat of extinction. IUCN (1994) Red List status LR cd.
Photo Ken Hill
Photo Ken Hill


Stems arborescent to acaulescent, to 1.5 m tall, 14-20 cm diam. at narrowest point.

Leaves bright green to deep green, semiglossy, 60-120 cm long, flat (not keeled) in section (opposing leaflets inserted at 170-180° on rachis), with 140-280 leaflets, with white, orange or brown tomentum persistent above and below; rachis frequently terminated by a spine 1-18 mm long. Petiole 11-31 cm long (15-30% of total leaf), petiole pubescent, spinescent for 10-90% of length. Basal leaflets gradually reducing to spines, 10-50 mm long.

Median leaflets simple, strongly discolorous, 80-145 mm long, 5-8 mm wide, inserted at 55-80° to rachis, decurrent for 2-4 mm, narrowed to 3-5 mm at base (to 50-70% of maximum width), 5-10 mm apart on rachis; median leaflets section flat; margins slightly recurved; apex acute, spinescent; midrib flat above to raised above, raised below.

Cataphylls linear, pungent, pilose, 60-70 mm long, persistent.

Pollen cones narrowly ovoid, orange to brown, 10-24 cm long, 5-7.5 cm diam.; microsporophyll lamina firm, not dorsiventrally thickened, 19-30 mm long, 11-17 mm wide, fertile zone 13-22 mm long, sterile apex 5-8 mm long, level, apical spine prominent, sharply upturned, 7-14 mm long.

Megasporophylls 6-11 cm long, brown-tomentose; ovules 2, glabrous; lamina orbicular, 60-110 mm long, 30-80 mm wide, deeply pectinate, with 22-46 soft lateral spines 8-35 mm long, 1-2 mm wide, apical spine distinct from lateral spines, 23-45 mm long, 4-8 mm wide at base.

Seeds subglobose, 30-37 mm long, 26-37 mm wide; sarcotesta yellow, not pruinose, 2-3 mm thick; fibrous layer present; sclerotesta smooth. Spongy endocarp absent.

The Cycad Pages

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Written and maintained by Ken Hill 1998-2010
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