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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Pseudoxytenanthera Soderstrom and Ellis

~ Dendrocalamus, Oxytenanthera (Dendrocalamus monadelphus Thwaites, Oxytenanthera thwaitesii Munro, Oxytenanthera monadelpha (Thwaites) Alston)

Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms 400–800 cm high; woody and persistent (stout and soft below, bending over and becoming thin and whiplike towards their tips); to 1.5 cm in diameter; ‘vinelike’; branched above. Buds from which the primary culm branches arise (where recorded) 1. Primary branches in P. monadelpha 11–20; clumped. Culm leaf sheaths present; conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades lanceolate, or triangular. Pluricaespitose. Rhizomes pachymorph. Plants unarmed. Young shoots extravaginal. Leaves not basally aggregated; with auricular setae. Leaf blades linear-lanceolate (acuminate); broad; 20–30 mm wide (and 12–20 cm long); flat; pseudopetiolate; without cross venation; where recorded, disarticulating from the sheaths; rolled in bud. Ligule in the form of a hard ridge with a curved, denticulate margin; truncate; 1.3–1.7 mm long. Contra-ligule present (in the form of a ciliolate ridge).

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence indeterminate (the spikelets each with two gemmiferous bracts beneath the glumes); with pseudospikelets; a spicate, leafless branch with sessile clusters of pseudospikelets; spatheate. Spikelet-bearing axes capitate (the clusters spaced along the main axis). Spikelets (i.e. the pseudospikelets) not secund; sessile.

Female-fertile spikelets. Spikelets unconventional; 13–16 mm long; lanceolate, or ovate, or linear; compressed laterally to not noticeably compressed (?); falling with the glumes; not disarticulating between the florets (the spikelet falling entire). Rachilla prolonged beyond the uppermost female-fertile floret.

Glumes two; very unequal (the upper longer); shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous (but ciliate along the middle and upper margins); pointed; awnless; similar (obovate-triangular, becoming thickened towards the pointed tips). Lower glume 10–11 nerved. Upper glume 10–11 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless. Spikelets without proximal incomplete florets.

Female-fertile florets 1–2 (i.e. 1–3 florets, with acropetal reduction). Lemmas obovate-triangular, thickened above; similar in texture to the glumes; entire; pointed; awnless to mucronate; hairless; glabrous; without a germination flap; 13–16 nerved (with transverse veinlets). Palea present; relatively long (a little shorter than the lemma); not convolute; entire; awnless, without apical setae; thinner than the lemma; not indurated; several nerved (7 – 3 between the keels and one on each side); 2-keeled. Palea keels wingless; hairy (ciliate). Lodicules absent. Stamens 6; monadelphous. Anthers about 3 mm long (orange); penicillate; with the connective apically prolonged. Ovary apically glabrous (but the style pilose); with a conspicuous apical appendage (and a hollow style). The appendage long, stiff and tapering. Styles fused. Stigmas 2, or 3.

Fruit, embryo and seedling. Fruit medium sized (about 5 mm long); fusiform; not noticeably compressed (plano-convex). Hilum long-linear (dark, almost the length of the fruit). Pericarp thick and hard (above, but thinner and easily separable from the seed below); loosely adherent (below), or fused (above). Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae over-arching the stomata (and obscuring them); several per cell (with one to two rows of 8–12 per long-cell). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies predominantly saddle shaped (a large version of this form); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade (of arm-cells); with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat (except near the midrib). Midrib conspicuous; having complex vascularization. The lamina distinctly asymmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Bambusinae. 1 species.

Distribution, phytogeography, ecology. Southern India and Sri Lanka.

Rusts and smuts. Smuts from Tilletiaceae (the large central bud remains dormant while the laterals produce numerous basal branches, then subsequently develops into a long, whiplike branch producing clusters of branches at each node).

References, etc. Morphological/taxonomic: Soderstrom and Ellis 1988. Leaf anatomical: Soderstrom and Ellis 1988; studied by us - P. monadelphia (Thwait.) Soderstrom & Ellis.

Illustrations. • P. monadelpha, vegetative: Soderstrom & Ellis (1988). • P. monadelpha, detailed morphology: Soderstrom & Ellis (1988). • P. monadelpha, leaf anatomy: Soderstrom & Ellis (1988)

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.