Schizostachyum sp. (TH: Kanchanaburi)

Distribution: THAILAND (West): Kanchanaburi Province. Also known from Tak Province, where the species flowered in the 2010s (Mu Chakkrapong, pers. comm., Facebook, 26 Mar. 2021).

Characteristics: Habit tight caespitose. Rhizome pachymorph, short. Culms straight, erect or slightly bending below, strongly bending or arching above; longer than 6 m [ultimate length not yet known]. Young shoots green, with spreading green culm-leaf blades; emerge April – November. Culm-internodes terete, 55–83 cm long, mid-green, initially scaberulous, becoming glabrous and smooth soon, not farinose; diameter 1.5 cm [ultimate diameter not yet known]; walls thin, lacuna filled with white pith, but a small cavity remains. Culm-nodes glabrous, smooth, slightly prominent; sheath scar 1–2 mm high, marginally protruding; supranodal line obscure, without a ridge; with a white, non-farinose, about 2 cm tall ring below the sheath scar, the ring color fading with age, and with a few short rigid appressed black hairs; aerial roots none. Branch-buds solitary, from the basal node up. Branches initially 2–9, with the central one usually somewhat dominant on the mid-culm, several small unequal to subequal branches of different lengths develop on the upper culm, usually none of them very dominant; occasionally a single, long and very dominant branch develops negative-phototropic, almost as thick as the main culm; unbranched on the basal and lower culm; branching intravaginal or infravaginal; rebranching. Culm-leaves persistent and decaying on the lower unbranched culm, deciduous on the mid-culm and the upper (branched) culm. Culm-leaf sheaths 6–7 cm wide at the base, 14–19 cm long, shorter than the internode; thickly papery, mid-green to light green when young, light straw colored when dry, then becoming dark brownish mottled, scattered with short pale hairs when young, becoming glabrous soon, smooth or slightly rough; margins initially pale ciliate, becoming glabrous soon; apex 10–12 mm wide, horizontal-truncate or slightly convex rounded. Culm-leaf auricles low inconspicuous rims, dark green to blackish green when young, with straight or waved 6 mm long pale late caducous bristles. Culm-leaf ligule 0.5–1 mm high, inconspicuous, subentire, with a few short pale caducous bristles when young. Culm-leaf blades papery, caducous, patent when young, strongly reflexed when old, green when young, light straw-colored when dry, narrowly lanceolate, 6–14 cm long, usually half as long as the sheath at mid-culm; junction with the sheath apex 5 mm wide; margins convolute from an early stage of development; apex long pointed. Foliage-leaves (3) 7–8 (10) per branchlet. Foliage-leaf sheaths keeled, mid-green to light green, initially with short pale hirsute and tomentose hairs, becoming glabrous and smooth soon; margins eciliate or ciliolate; apex reddish when young. Foliage-leaf auricles inconspicuous rims, mid-green to dark green when young; with erect 10–15 mm long pale bristles. Foliage-leaf ligule inconspicuous, less than 1 mm high, entire. Foliage-leaf blades tough, medium-sized, (16) 23–32 (40) × 4–7 cm, lanceolate to broadly lanceolate, mid-green and glabrous on both surfaces; base unequal, usually wedge-shaped, rarely rounded; apex attenuate; margins antrorsely scabrous to scaberulous; midrib proximally prominent and light green beneath; pseudopetiole 5–12 mm long. Flowers are known [not dissected], protogynous. Spikelets 2–4 cm long, brown to reddish brown, short pale hispid, in tufts of 5–12 spikelets, 3–15 cm apart, on leafless branches and terminating leafy branches. Style long and thin, hollow; stigmas 3, short, bent, hispid, whitish and pinkish. Stamens 6, thread-like, flat, becoming twisted, green (the central axis) and reddish or reddish-brown (the parts twisted around the axis), ca. 18 mm long; apex pointed; filaments white, fused to a tube. Seed: Caryopsis, long-ovoid, ca. 2 cm long and 3.5–4.5 mm thick, longitudinally slightly grooved; pericarp thin, glossy, adnate to the seed; apex with a long style permanently attached.

Flowering and seeding: Flowering was initiated in late March 2021, and in April it became apparent that flowering is gregarious. All leafy branches developed into flowering branches but contained still abundant foliage-leaves in mid-June 2021. Florets with fully developed, ripe seeds are rare.
The first batch of spikelets collected from May to 10 June 2021:
(1) Empty spikelets or spikelets with fruits obviously non-matured, naturally dropped off and collected from the ground in huge numbers, possibly far more than one thousand, 10 spikelets weighing ca. 0.3–0.55 g.
(2) Spikelets that might contain fruits but were possibly not fully matured, naturally dropped off, and 69 collected from the ground, spikelet width 3–5 mm, 10 spikelets weighing ca. 0.7–0.8 g.
(3) Spikelets obviously containing fully developed and ripe fruits, only 30 collected, 26 of which were collected from the ground, 4 directly from flowering branches (it later turned out that these 4 were not fully developed), spikelet length ca. 4.0–4.6 cm, width 4.5–5.5 mm, 10 spikelets weighing ca. 2.0–2.4 g.
The second batch of spikelets was collected from 11 June to 13 July yielded 268 seeds weighing 66.3 g (100 seeds ≈ 25 g).
The third batch of seed-bearing spikelets was collected from 14 July until and including August 2021.

Seed viability: Unknown, viability is assumed to last 1–2 months.

Seed weight: 10 ca. 2-week dried spikelets (husk-wrapped seeds) = 2.0–2.4 g.

Seed germination: 5 seeds bare of husks set in moistened coir dust on 11 June 2021; coleoptiles of 3 seeds emerged after 11 days, and a 4th coleoptile on the 21st day, hence, 4 of 5 seeds germinated (seed germination test 210611).

Cultivation requirements: Grows well in part shade on heavy moisture-retentive soil with good drainage.

Comments:

(1) BS-0573 has tentatively been assigned to Schizostachyum. BS-0573 seems to be closest to Schizostachyum strictum, syn. Neohouzeaua stricta, from Myanmar. However, the description of the vegetative parts of Schizostachyum strictum is rather brief and not detailed enough for proper identification when flowers are unavailable. Foliage-leaf auricles are described as "falcate" in Schizostachyum strictum, whereas in BS-0573 they are long rims but very low, thus inconspicuous.

(2) The vegetative characteristics of BS-0573 were also compared to those of Bambusa schizostachyoides (syn. Schizostachyum kurzii, Pseudobambusa kurzii). Although the vegetative characteristics of Bambusa schizostachyoides have only been described incompletely, it can be ruled out that BS-0573 is this species. For example, it is very unlikely that BS-0573 will reach a culm diameter of up to 10 cm, as in B. schizostachyoides. Furthermore, the foliage-leaf sheath auricles of BS-0573 are rim-like, while those of B. schizostachyoides are falcate. In addition, the foliage-leaf blades of BS-0573 are significantly larger, and the pseudopetioles significantly longer than in B. schizostachyoides.

(3) BS-0573 has some peculiar characteristics, some of which are rare in Schizostachyum, others are not known to occur in Schizostachyum. The partial absence of fuzz on the internodes has been observed in some Thai species assigned to Schizostachyum, whereas the complete lack of fuzz as in BS-0573 is not known in this genus. The presence of pith in the cavity of the internodes has been recorded in some species of Schizostachyum, e.g., Schizostachyum kerrianum, syn. Neohouzeaua kerriana, but seems to be very rare in other species of Schizostachyum.

(4) The species is easily distinguishable from similar species by its convolute culm-leaf blades (in an early green stage as well as in the dried stage), which are strongly reflexed when dry. Further notable characteristics are the glabrous culm-internodes in mature culms (in Schizostachyum species, the internodes are evenly covered with fuzz even in the mature stage), and the broad white ring below the nodes. This white ring is neither mealy nor waxy, and is not sericeous. The white color can not be rubbed away, but it fades with age. The branch complement of unequal rather than subequal branches, and the potential of developing a single upright branch almost as thick as the main branch, have been observed in at least one other species of Schizostachyum.