ruak

Thyrsostachys siamensis Gamble
Common name: Ruak, Pai Ruak, Wae-pang, Wae-bang, Sa-lom, Huak, (Smitinand,
2001). Thailand Bamboo, Monastery Bamboo (Ohrnberger, 1999).
T. siamensis is the most well known and most extensively grown bamboo in Thailand.
The number of common names exhibits its large range of habitat and climates. This
member of the Bambuseae does very well in poor soil conditions. Native range
includes Thailand, Burma, and possibly parts of Lao (Bennet, 1988).

Thyrsostachys siamensis is a densely sympodial, densely tufted bamboo endemic to
northern and northeastern Thailand. Culms are erect with arched tips. Nodes are not
swollen but have white rings directly below. Each internode is 15-30 cm in length with
very thick to solid walls at the base and thinning toward the top. Branches arise from
mid-culm upwards and consist of one dominant branch and several smaller branches
per node. 8-14 meters high and 2-7.5cm in diameter, the grayish green culms are
usually covered by persistent culm sheaths. Culm sheaths are 20-25 cm long and
10-20 cm wide near the base and narrowing up to 2.5 cm at the apex. The culm
sheath is covered with scattered, pale, appressed hairs. Pale to purple green at first,
they slowly turn stramineous and thin with age. The blade is narrowly lanceolate, 6-15
cm by 5-12 mm, erect and pubescent adaxially. The ligule is very short, shortly
laciniate and has no or very small auricles. Leaf blades are linear, narrow, 7-14 cm by
5-8 mm, pale green and usually glabrous. Leaf sheath is striate, white and hairy along
the margins. The ligule is very short and ciliate. Auricles are absent or very short.
Inflorescence is borne on both leafy and/or leafless branches consisting of a main
branch and many thin branchlets bearing bracteate clusters of few pseudo spikelets.
The spikelet is about 17 mm long and is comprised of one empty glume, usually 2
perfect florets and a rachilla extension bearing a rudimentary floret. Flowering is
normally sporadic and gregarious flowerings are rare. Flowering usually occurs during
the dry season. T. siamensis usually dies after flowering (Dransfield, 1995)