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The grass genera of the world

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

Lasiorhachis (Hack.) Stapf

~ Saccharum

Including Lasiorrachis Stapf

Habit, vegetative morphology. Perennial; caespitose. Culms 50–100 cm high; herbaceous; unbranched above. Culm nodes exposed; hairy. Culm leaves present. Culm internodes solid. Young shoots extravaginal. Leaves mostly basal; non-auriculate (hairy at the auricle positions). Leaf blades linear to linear-lanceolate; harsh; narrow; 5–10 mm wide; flat, or rolled (involute); pseudopetiolate (attenuate to the base, cf. Imperata cylindrica); without cross venation; persistent. Ligule an unfringed membrane; not truncate; 0.7–1 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (at least towards the tips of the inflorescence branches); hermaphrodite, male-only, and sterile (in the material seen), or hermaphrodite and male-only (in other collections, according to Stapf 1926); overtly heteromorphic, or overtly heteromorphic to homomorphic; in both homogamous and heterogamous combinations (homogamous below, heterogamous above).

Inflorescence. Inflorescence paniculate (pilose, with white hairs); open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes paniculate; the spikelet-bearing axes with more than 10 spikelet-bearing ‘articles’; with very slender rachides (these not channelled); disarticulating; disarticulating at the joints. ‘Articles’ linear; without a basal callus-knob; not appendaged; disarticulating transversely; densely long-hairy. Spikelets paired; not secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite, male-only, and sterile (in the material seen, the much reduced members at the tips of the branches), or hermaphrodite and male-only (all or nearly all male, in some specimens).

Female-sterile spikelets. The pedicelled spikelets falling from their pedicels, apparently very variable in sexuality and completeness, hermaphrodite to male or rudimentary, sometimes with two functional male florets in the material seen.

Female-fertile spikelets. Spikelets 4–6 mm long; elliptic to lanceolate; compressed dorsiventrally; planoconvex; falling with the glumes (and in the case of sessile spikelets, with the associated rachis joint and pedicel). Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short (hairy in both sessile and pedicellate spikelets); blunt (truncate).

Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; hairy (both pilose); (the upper) pointed; awnless; (the upper) carinate; very dissimilar (both firmly membranous or papery, G1 bicarinate, G2 naviculate). Lower glume two-keeled; convex on the back to flattened on the back; relatively smooth; 6–9 nerved. Upper glume 5–7 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; 2 nerved, or 3 nerved, or 5 nerved; more or less equalling the female-fertile lemmas, or decidedly exceeding the female-fertile lemmas; decidedly firmer than the female-fertile lemmas (membranous with hyaline wings); not becoming indurated.

Female-fertile florets 1. Lemmas broad; less firm than the glumes (membranous or hyaline); not becoming indurated; entire to incised; when incised, 2 lobed; not deeply cleft (no more than minutely incised); mucronate to awned. Awns when present, 1; median; from a sinus, or apical; non-geniculate; straight; hairless; much shorter than the body of the lemma; entered by one vein. Awn bases not twisted; not flattened. Lemmas hairy (along the margins only); non-carinate; without a germination flap; 1 nerved, or 3 nerved. Palea present; conspicuous but relatively short; apically notched; awnless, without apical setae (but ciliate); textured like the lemma; not indurated; inconspicuously 2-nerved, or nerveless; keel-less. Lodicules present; 2; free; fleshy; ciliate (on their points, with deciduous needlike hairs, in the material seen). Stamens 3. Anthers about 2 mm long; minutely penicillate; without an apically prolonged connective. Ovary apically hairy (on the appendage (q.v.), the hairs resembling those on the lodicules); with a conspicuous apical appendage (all those examined with a rather to very conspicuous, linear, hairy appendage, perhaps representing a vestigial style but originating distinctly lower on the apex than the normal pair). Styles free to their bases. Stigmas 2 (the putative vestigial style without stigmatic papillae); red pigmented.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower and more uniform); of similar wall thickness costally and intercostally (thin walled). Intercostal zones with typical long-cells, or exhibiting many atypical long-cells (isodiametric to square, in places). Mid-intercostal long-cells rectangular (to rhomboid); mostly having markedly sinuous walls. Microhairs present (large); elongated; clearly two-celled; panicoid-type. Microhair apical cell/total length ratio about 0.5. Stomata common. Subsidiaries non-papillate; high dome-shaped to triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. No macrohairs or prickles seen. Costal zones with short-cells. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (pairs or short rows). Costal silica bodies present and well developed (in places, but lacking in others); ‘panicoid-type’; short dumb-bell shaped (mostly), or cross shaped.

Transverse section of leaf blade, physiology. C4. The anatomical organization conventional. XyMS– (the PCR cell walls often thick, mestome sheath-like). PCR sheath outlines uneven. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (in places, associated with the bulliform-plus-colourless cell arches). Leaf blade adaxially flat. Midrib very conspicuous; having a conventional arc of bundles (these numerous, abaxial); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans; associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the major bundles); forming ‘figures’ (large I’s). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; cf. Andropogoneae (?). 1 species.

Distribution, phytogeography, ecology. Madagascar.

References, etc. Leaf anatomical: this project.

Special comments. Description restricted to L. hildebrandtii (Hack.) Stapf. Stapf’s (1926) dismissal of the hairy ovary apex is untenable, and Bosser’s association of two Miscanthidium species with L. hildebrandtii is unconvincing. The material seen (Hildebrandt 3755) has most of the pedicellate spikelets male, except near the baranch tips. ‘Glabrous’ lodicules (seen in some of the florets examined, cf. Bosser 1968) may reflect easily dislodged hairs (observed in other florets). Fruit data wanting.


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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: 13th November 2017. delta-intkey.com/grass’.

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