×Thyrsocalamus sp. aff. ×T. liang

Distribution: THAILAND (North), cultivated.

Specimens: BS-0347 [†] (living plant), from Ban Pho Thong Charoen, Doi Saket District, Chiang Mai Province, 11 Dec. 2009, cult., received as ไผ่รวกดำ (phai ruak dam), started flowering in late Dec. 2014 and died in mid-2016; BS-0234 [†] (living plant), 1 Aug. 2009, and BS-0396 (culm-leaf), 10 Jan. 2010, both from the same clump from Ban Pa Fang, Doi Saket District, Chiang Mai Province, cult., received as ไผ่รวกดำ (phai ruak dam), started flowering in Jan. 2017 and died in mid-2017.

Characteristics: Habit a tight erect clumper. Rhizome pachymorph, short-necked. Culms straight upright, the basal and lower culm typically unbranched, height 20 m or a little over, diameter 4 (5) cm. Young shoots dull dark green, emerge usually from late July to September. Culm-internodes dull dark green, white mealy velvety on the lower section, glabrous or nearly so on the upper section [bright dark green in phai liang dam, bright mid-green in phai liang wan], (30) 35 (40) cm long, thick-walled, solid or nearly so on the lower culm (7th internode 88 cm above the ground, 4.0 cm in diameter with a 1.2 cm thick wall). Culm-nodes not prominent, with a narrow white ring below the sheath scar. Branch-buds as tall as broad, or slightly taller than broad [broader than tall in phai liang wan, much broader than tall in phai liang dam]. Branches many, the central one dominant, branching intravaginal. Culm-leaves on the basal and lower culm either persistent and decaying on the culm (rotten sheath remnants may remain attached), or (late) deciduous [typically early deciduous in phai liang, typically persistent in Thyrsostachys siamensis]; culm-leaves of the mid and upper culm deciduous; culm-leaves whitish when dry. Culm-leaf sheath sparsely covered with short white mealy velvety hairs; apex truncate, slightly convex-waved. Culm-leaf auricles small, oral hairs few, short, early deciduous. Culm-leaf ligule short, entire, eciliate. Culm-leaf blade broad-triangular, erect (typically not reflexed), persistent or late deciduous, glabrous. Foliage-leaves (5) 7–10 (13) per branchlet. Foliage-leaf sheath glabrous. Foliage-leaf auricles none; oral setae none. Foliage-leaf ligule inconspicuous. Foliage-leaf blades mid-green to dark green, small and narrow, (7) 11 (14) × (0.8) 1.0 (1.5) cm, glabrous on both surfaces; margins slightly antrorsely scabrous; pseudopetiole 1 mm long.

Uses: Culms for construction and tools; plants for hedges, screening, and windbreaks.

Cultivation requirements: Easy-growing; in part shade to full sun, sandy loam to clay loam, moisture-retentive, can resist some drought.

Provisional identification:

(1) This species has remained unidentified so far. At first sight, it has been assumed to be Thyrsostachys oliveri. In general appearance, this bamboo (BS-0347, BS-0234) shows the closest similarity to Thyrsostachys, but culm-leaves are different, chiefly by their presence of small though clearly visible auricles, and they do not closely match Gamble's original description and line drawing of the culm-leaves of Thyrsostachys oliveri (J. S. Gamble, Bambuseae Brit. India, 1896: p. 58–59 [#1230]). There is also some similarity with phai liang, which was identified as an intergeneric hybrid ×Thyrsocalamus, and similarity with Dendrocalamus strictus. The plants (BS-0347, BS-0234) are certainly neither conspecific with ×Thyrsocalamus liang, nor with Dendrocalamus strictus. The plants (BS-0347, BS-0234) can be clearly distinguished from all known variants of ×Thyrsocalamus liang.

(2) From the time BS-0347 flowered, and somewhat later BS-0234, it became clear that this species belongs to the Bambusa-Dendrocalamus-Gigantochloa complex, and is not conspecific with any of the aforementioned species. It was noted that the inflorescence of the plants (BS-0347, BS-0234) is similar to that of Thyrsostachys. However, flowers have not yet been investigated in detail enough to identify the species. Anthers are yellowish, with free filaments, whereas anthers are red in ×Thyrsocalamus liang. As for the vegetative parts, a main unresolved obstacle in placing this species into the genus Thyrsostachys is the difference in culm-leaf characteristics between the description (and line drawing) by Gamble, and the observed characteristics in the plants (BS-0347, BS-0234).

Flowering and seeding: Neither seeds in the flowers nor seedlings on the ground were found. This indicates a possible hybrid origin, and one of the parents could be Thyrsostachys.

(1) BS-0347: Prior to flowering, the plant had grown to near maximum culm height and diameter. Gregarious flowering initially started with only 3 culms in late December 2014, with the flowering peak in early 2015. The three culms died and were cut off in mid-2015. New thick shoots emerged from the clump untimely in early April 2015 and developed into 20 m tall culms. The clump did not cease vegetative growth, and no signs of further flowering were observed by late October 2015, but one month later, the whole clump continued gregarious flowering and was dead by mid-to-late 2016. No seeds were found in the flowers, and no seedlings were found on the ground (27 Apr. 2017).

(2) BS-0234: Prior to flowering, the plant had grown to about two-thirds of its maximum culm height and diameter. Gregarious flowering of all culms started in January 2017 (first observed on 26 Feb. 2017), with the flowering peak in mid-March 2017. At the end of April 2017, the clump seemed to have died. No seeds were found in the flowers, and no seedlings were found on the ground (27 Apr. 2017).

Specimen: BS-0927 [-] (herbarium material), from Samoeng District, Chiang Mai Province, coll. by ธ. บ., s.n., Feb. 2018, received 23 Feb. 2018.