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The grass genera of the world

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

Polytoca R.Br.

Including Cyathorhachis Steud.

Habit, vegetative morphology. Tall, robust perennial, or annual; caespitose. Culms 120–250 cm high. Culm nodes hairy, or glabrous. Culm internodes solid (sometimes compressed). Leaves not basally aggregated; auriculate, or non-auriculate. Leaf blades broad; 8–60 mm wide; flat; pseudopetiolate, or not pseudopetiolate; without cross venation; persistent. Ligule present; an unfringed membrane.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only, male-only, and sterile. The male and female-fertile spikelets in different inflorescences and segregated, in different parts of the same inflorescence branch, or segregated, in different parts of the same inflorescence branch (male spikelets in the slender, upper part of the raceme, the females below, sometimes with some racemes all male, the latter often grouped in a terminal panicle). The spikelets overtly heteromorphic, or overtly heteromorphic and homomorphic (male, female and rudimentary, the pedicellate spikelets in both male and female parts of the inflorescence sometimes with the G1 awned); in both homogamous and heterogamous combinations and all in heterogamous combinations, or all in heterogamous combinations.

Inflorescence. Inflorescence of terminal and axillary spicate racemes; digitate and non-digitate (the terminal, male racemes digitate or in a racemose panicle), or non-digitate (lateral, a single raceme). Rachides hollowed. Inflorescence spatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’ (peduncled); solitary; with substantial rachides; disarticulating (at least in the female part); disarticulating at the joints (in the lower, female part). ‘Articles’ (of female segments) non-linear (widened and hollowed above); with a basal callus-knob. Spikelets paired; secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis (wholly or in part). The ‘shorter’ spikelets female-only (in the lower part of the raceme), or male-only (above and in male racemes). The ‘longer’ spikelets sterile, or female-only and sterile (in the female part of the raceme), or male-only (?), or sterile (in the male part of the raceme, and male racemes).

Female-sterile spikelets. Pedicelled partners of the (sessile) female spikelets well developed but barren, or reduced. Male spikelets with membranous glumes and two male florets. The male spikelets with glumes; 2 floreted (both fertile).

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large; more or less equal; long relative to the adjacent lemmas; awnless; very dissimilar (G1 obtuse or emarginate, indurated below, G2 acuminate). Lower glume not two-keeled (often winged above); convex on the back; 17–19 nerved. Upper glume 8–19 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 3–7 nerved; not becoming indurated (thin, acuminate).

Female-fertile florets 1. Lemmas less firm than the glumes (thinly membranous); not becoming indurated; awnless; hairless; non-carinate; 3 nerved. Palea present; textured like the lemma; not indurated; 2-nerved. Lodicules absent. Stamens 0. Ovary apically glabrous. Styles basally fused. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit longitudinally grooved (and hollowed at the base). Hilum short (in the basal hollow). Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (57–)66–75(–76.5) microns long; (9–)9.6–10.5(–11.4) microns wide at the septum. Microhair total length/width at septum 5.9–7.8. Microhair apical cells (39–)42–52.5(–54) microns long. Microhair apical cell/total length ratio 0.64–0.75. Stomata common; (45–)48–54(–60) microns long. Subsidiaries dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped and dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with non-radiate chlorenchyma; with arm cells (apparently some, but not completely convincing), or without arm cells (?). Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. 2n = 20 and 40.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Maydeae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Chionachninae. 2 species.

Distribution, phytogeography, ecology. Indomalayan region.

Mesophytic. Forest margins.

References, etc. Leaf anatomical: studied by us - P. macrophylla Benth.

Illustrations. • P. digitata: Wu Zhengyi, Flora Yunnanica 9 (2003). • P. macrophylla, abaxial epidermis of leaf blade: this project. • Abaxial epidermal leaf blade detail of Polytoca macrophylla: this project

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.’.