Dendrocalamus khoonmengii

Thai names: ไผ่กระโรม (phai kra rom); ไผ่ปูนผาตากผ้า (phai pun pha tak pha); "phai mung". — T. Smitinand, 2001 [#1003]; BKF [#1368].

Distribution: THAILAND (South): Nakhon Si Thammarat Province: Khao Luang National Park, on steep slopes by the river, at 100 m altitude.

Description: "Rhizomes pachymorph. Culms unicaespitose, in a loose clump, up to 13 m long, 3–4 cm in diam., with relatively thin walls, culm tips strongly arching over; internodes 35–50 cm long, plain green, copiously white-waxy all over in very young stages, glabrous and waxless when older, lower internodes not covered with hairs; nodes not swollen, lower nodes without verticils of roots, the region directly below each node of young culm with a band of black hairs. Branches developing from mid-culm or from lower quarter upwards; branch complement at mid-culm of one dominant primary axis with two secondary, weaker axes from its base and several smaller higher-order branchlets, the dominant primary axis long and slender, reaching 3–5 m long, much longer than other axes; without aerial roots. Culm-sheaths pale pinkish to greenish to orange, covered with black hairs mainly on the lower half and copious white wax all over, deciduous, coriaceous, 15–25 by 10–15 cm, top convexly truncate; blades green, narrowly lanceolate, spreading to reflexed, 15–20 by ca 2 cm (width near the base), sparsely hairy near the base on the adaxial surface; auricles purplish-black, lobe-like, 1–1.5 by 0.2–0.7 cm, somewhat curved, slightly twisted, and free at the ends, margin with pale brown bristles to 7–10 mm long; ligule pinkish purple, 3–12 mm long, irregularly toothed, some divisions further divided into fine bristles, about 5 mm long. Leaves 5–10 per branch; leaf blades narrow, 5–12 by 0.4–1.2 cm, upper surface glabrous to sparsely hairy, lower surface glaucous and covered with short and fine hairs and scattered with long hairs to 1 mm long, apex acuminate, margin serrate, base rounded to oblique-cuneate; sessile or with pseudopetiole to 1 mm long; auricles absent or just tiny rims, fringed with a few wavy bristles to 3.5 mm long; ligule about 0.1–0.3 mm long, irregularly toothed; secondary veins 2–4 pairs, intermediate veins 4–7; leaf sheaths 2–3 cm long, hairy. Inflorescences unknown." — S. Sungkaew & al., in Thai Forest Bulletin (Botany), 35, 2007: p. 98-102 [#1060].

Images: Line drawing in S. Sungkaew & al., in Thai Forest Bulletin (Botany), 35, 2007: p. 100 [#1060]. Photo in S. Sungkaew, BRT Biodiversity (shoot) [#1343], and in Kasetsart Univ. Forestry (shoot).

Characteristics: Similar species are Dendrocalamus pendulus, Dendrocalamus hirtellus, Dendrocalamus dumosus, and Dendrocalamus elegans. The primary distinctive characteristics of Dendrocalamus khoonmengii "are its projecting, curved and lightly twisted culm sheath auricles, and its abaxially glaucous leaf blades" (S. Sungkaew & al., l.c., 2007: p. 102-103 [#1060]). The auricles can be seen from the line drawing (S. Sungkaew & al., l.c., 2007: fig. 1, p. 100 [#1060]).

Comments:

(1) Flowers were unknown when the species was published in 2007. By late 2016, no records of flowering and seeding of this species were known (Sarawood Sungkaew, pers. comm., 20 Dec. 2016).

(2) The species was named in honor of Khoon Meng Wong, a botanist from Malaysia.

(3) Several plants (BS-0541, BS-0358), received under the name Dendrocalamus khoonmengii from the wild of Satun Province in 2010, still need to be examined to determine if they truly represent this species or, more likely, represent a different species.

Comments: The following specimens (BS-0541 etc., BS-0288, etc., BS-0700, etc., BS-0531, BS-0532) have been provisionally placed near Dendrocalamus khoonmengii for their overall similarities with this species, and mainly for their conspicuous protruding culm-leaf auricles. However, the shape of the culm-leaf auricles is different (but seems neither to fit with Dendrocalamus dumosus and Dendrocalamus elegans), flowers and seeds are known from 3 specimens (whereas flowers and seeds are unknown in Dendrocalamus khoonmengii), and culm and branch internodes are solid to moderately thick-walled (but thin-walled in Dendrocalamus khoonmengii).

Cultivation requirements: Plants grow well on normal garden soil with a neutral pH. A test revealed that plants (seedlings of BS-0541B) also grow well on highly alkaline soil (10 pH).

Seed weight: 10 g ≈ 650–730 dried spikelets (husk-wrapped seeds).

Seed viability: Over 1 year.

Seed germination: (1) Seeds (BS-0541A) placed on moistened tissue paper, in late January 2012, 24–31 °C day, diffuse light, 12–20 °C night, atmospheric humidity >70%, the first shoot emerged after 17 days, possibly delayed by initially low temperatures. The germination rate was very high (>95%, by early April 2012). The germination rate was over 70% in October 2012, and over 40% in March 2013. — (2) 10 seeds (BS-0541B) placed on moistened tissue paper, 31–36 °C day, diffuse light, 20–25 °C night, atmospheric humidity >70%, the first shoot emerged on the 4th day, 5 seeds have sprouted by the 7th day, 9 by the 12th day (test 140407). — (3) pH tolerability test (Jul. – Sep. 2014): Seedlings (BS-0541B) grow well on a high alkaline growth medium (10 pH).

Comments:

(1) Several plants of the Satun population were received in 2010, of which all but one flowered (starting Nov. 2011) and died (the last plant in June 2013). The first seeds were collected on 27 Jan. 2012, and the latest seeds in mid-2013. Seedlings were raised (BS-0541A). The single, hitherto non-flowering plant started flowering (in late 2013) and, after seeding, died (mid-2014). Seeds were collected on 29 Jan., 10 Mar., 19 Apr., and 8 May 2014, and seedlings were raised (BS-0541B). The seedlings turned out to be robust plants, growing well on normal garden soil (Aug. 2013).

(2) Characteristics of the culm sheath, e.g., length and auricles, are different from all the other plants assigned to Dendrocalamus dumosus and D. elegans, whereas other vegetative characteristics are rather similar.

(3) The characteristics recognized on immature plants are similar to Dendrocalamus khoonmengii, except internodes are (moderately) thick-walled to solid, aerial roots may occur on basal culms in plants of the Satun population, and the flowers of D. khoonmengii are still unknown, hence not yet described. When the plant matured, it became unlikely that BS-0541 represented D. dumosus, as the culm sheaths developed projecting, curved auricles.

(4) Seeds from plants of the Satun population are morphologically similar to Dendrocalamus membranaceus and D. barbatus, but are much smaller, and 100 seeds weigh only 1.4–1.5 g.

Specimens: BS-0700 [BBG, SSG], BS-0700-1 [S5], BS-0700-2 [-], BS-0700-3 [BBG] (living plants), raised from seeds (received 21 Mar. 2012) collected by ธ. ล. from the grounds (from the uppermost litter layer of the forest soil horizon, which contained numerous seeds) of a flowering, wild population in สตูล Satun Province, southern Thailand, without precise locality, in Feb./Mar. 2012. Assumed by ธ. ล. being "Dendrocalamus khoonmengii".

Characteristics: Habit caespitose. Rhizome pachymorph. Culms more than 6 m long [ultimate length not yet known], straight, erect below, bending and leaning above, top drooping. Young shoots usually emerge green, occasionally emerge deep brownish-green or blackish, then fade to dark green with age. Culm-internodes mid-green to dark green, glabrous, thinly farinose when young, slightly flattened on the bud-bearing side, 20–25 (30) cm long, diameter (1) 1.5–2.5 (2.7) cm [ultimate diameter not yet known]; culm-wall thickness varies, usually solid with a small lumen. Culm-nodes slightly prominent, sheath scar corky, blackish when young. Branch-bud solitary, subrotund, from the base up. Branches typically none on the basal and lower culm, 1 branch (rarely 2 branches) on the mid-culm, much dominant, 1/3 to 2/3 as thick as the main culm, elongating, upper culm with few to several thin subequal short branches; branching intravaginal. Culm-leaves deciduous. Culm-leaf sheath 1/4–1/2 as long as the internode of the lower culm, reddish when young, covered with blackish hairs (some hairs initially pale); apex truncate, junction with the blade about 1/3 the width of the apex. Culm-leaf auricles blackish when young, conspicuous, protruding, pale bristly, bristles 2–5 (–10?) mm long. Culm-leaf ligule short, 1 mm, orange-red when young (blackish in BS-0700-1), denticulate, with a few short pale bristles. Culm-leaf blade slightly to horizontally patent. Foliage-leaves 10–12 per branchlet. Foliage-leaf sheath glabrous. Foliage-leaf auricles conspicuous, caducous with age, blackish, with 5 mm long pale early caducous bristles. Foliage-leaf ligule short, 0.5 mm, blackish. Foliage-leaf blade glabrous on both surfaces, or sparsely pilose above and finely pubescent beneath when young, (9–) 12–21 × 1.2–2.0 cm, occasionally larger, to 23.5 cm long, to 2.9 cm wide, linear to linear-lanceolate, base rounded to wedge-shaped, margins antrorsely scabrous, apex long attenuate; pseudopetiole short, 1–2 mm.

Specimens: BS-0531 [†] (living plants) = CS-3031, Nai Han Beach (หาดในหาน), southern Phuket, southern Thailand, wild, received as "Dendrocalamus elegans", 26 May 2010; died because of flooding in 2017. BS-0532 [W3] (living plants) = CS-3032, same location.

Characteristics: Habit caespitose, a moderately tight clump. Rhizome pachymorph. Culms up to 18 m long or a little longer, erect below, bending and leaning above (→ table with culm size dimensions). Young shoots reddish, farinose, sparsely hairy; emerge from March to August/September. Culm-internodes thickly covered with a white mealy deposit when young, long-lasting, appearing bluish, green, and smooth when old, 28–46 cm long, diameter 2.5–3.2 cm on the basal and lower culm, slightly thicker on the mid-culm (from a height of about 2 m), thin-walled to moderately thick-walled only on the lower mid-culm, walls become relatively thicker and finally solid towards both the base and apex. Culm-nodes not or slightly prominent; sheath scar a somewhat corky ring, blackish when young. Branch-buds solitary, from the basal nodes up. Branches on the lower culm (for about 5 m) usually none, with 1–2 dominant elongating branches on the mid-culm and upper culm, with additional 2–3 thin subequal branches on the upper culm; branching intravaginal. Culm-leaves early deciduous. Culm-leaf sheaths about 1/2–3/4 as long as the internode, farinose and light green when young, straw-colored when dry, scattered with short dark hairs; margins short pale to dark ciliate; apex horizontally or concavely truncate. Culm-leaf auricles conspicuous sickle-shaped protruding lobes, blackish when young, margins with long straight or slightly waved pale bristles. Culm-leaf ligule short, blackish when young, denticulate, tapering into short straight pale bristles, edges with a few long straight pale bristles. Culm-leaf blades patent to reflexed, green when young. Foliage-leaves (5–) 7 (–13) per branchlet. Foliage-leaf sheaths minutely hairy when young, glabrous when old. Foliage-leaf auricles inconspicuous or lacking, without bristles. Foliage-leaf ligule inconspicuous, short, subentire. Foliage-leaf blades linear-lanceolate, 6–13 (18) × 0.7–1.0 (1.4) cm, glabrous above, pubescent(?) beneath when young, glabrous when old; base rounded to wedge-shaped; margins antrorsely scabrous; apex long-acuminate; pseudopetiole 0.5–1 mm. Flowers and seeds are unknown.

Comments: The above characteristics are based on 6-year-old plants grown from plant divisions, the culm length of 18 m was measured on 2 cut culms in July 2018.