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The grass genera of the world

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

Sclerachne R.Br.

~ Chionachne

Habit, vegetative morphology. Erect to prostrate annual. Culms 10–90 cm high; herbaceous. Culm internodes solid. Leaves non-auriculate. Leaf blades linear-lanceolate (with broad base and acute apex); broad; without cross venation.

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 segregated, in different parts of the same inflorescence branch (in terms of the reduced ‘racemes’), or mixed in the inflorescence (in terms of the panicle as a whole).

Inflorescence. Inflorescence paniculate (a complex pseudo-panicle: see Backer 1968); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes very much reduced (to peduncled, spatheate, spike-like reduced ‘racemes’ of 2(-3) spikelets: the first female, the terminal male, the middle if present male or female); paired to clustered (fascicled); with substantial rachides; disarticulating; falling entire (the peduncle apex widened, articulated with the hollowed base of the first spikelet). ‘Articles’ non-linear; disarticulating obliquely. Spikelets solitary, or paired; consistently in ‘long-and-short’ combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis. The ‘shorter’ spikelets female-only (basal), or male-only (terminal). The ‘longer’ spikelets sterile.

Female-sterile spikelets. The male spikelet terminal, with two equal herbaceous, acute, many-nerved glumes; two lemmas with male flowers, each having three stamens and two large lodicules. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; without proximal incomplete florets; 2 floreted. Male florets 2; 3 staminate.

Female-fertile spikelets. Spikelets falling with the glumes (and associated structures). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; long relative to the adjacent lemmas; hairless; awnless; very dissimilar (the G1 sheath-like, embracing base of raceme, indurated, 2-keeled, with one or two oblique transverse constrictions, emarginate and winged, the G2 ovate acuminate, transparent, indurated, grooved on each side of mid-nerve, its apex appressed to the keels of G1). Lower glume two-keeled. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; sterile. The proximal lemmas awnless; 3 nerved; similar in texture to the female-fertile lemmas (hyaline, but ovate, long-acuminate); not becoming indurated.

Female-fertile florets 1. Lemmas acute; less firm than the glumes (hyaline); not becoming indurated; entire; pointed; awnless; hairless; non-carinate; without a germination flap; 1 nerved (narrow). Palea present; entire (acute); awnless, without apical setae; 2-nerved. Lodicules absent. Stamens 0.

Fruit, embryo and seedling. Disseminule consisting of the disarticulated spikelet-bearing inflorescence unit (a false fruit, held together by the G1 of the basal, female spikelet). Fruit longitudinally grooved (on the back). Hilum short.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower, more regularly rectangular); of similar wall thickness costally and intercostally to differing markedly in wall thickness costally and intercostally (the costals somewhat thicker walled). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls and having straight or only gently undulating walls (pitted, the sinuosity where present fairly fine). Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries non-papillate; low dome-shaped to triangular (their outer walls unusually thick). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (but the raised cells calling for careful focusing); silicified. Intercostal silica bodies cross-shaped. No macrohairs or prickles seen. Costal short-cells conspicuously in long rows (over some veins), or predominantly paired (over others). Costal silica bodies present and well developed; ‘panicoid-type’; cross shaped to butterfly shaped, or dumb-bell shaped (short).

Transverse section of leaf blade, physiology. C4. The anatomical organization conventional. XyMS–. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms not reliably recordable in the material seen, but probably in the form of simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (only with the primaries, the sclerenchyma scanty save at the blade margins and abaxially in the midrib); forming ‘figures’ (small I’s or ‘anchors’ with the primaries). Sclerenchyma all associated with vascular bundles.

Cytology. 2n = 20.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Maydeae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Chionachninae. 1 species (S. punctata).

Distribution, phytogeography, ecology. Indo-Southeast Asia.

Forest margins.

References, etc. Leaf anatomical: studied by us.

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.’.