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The grass genera of the world

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

Lasiacis A. Hitchc.

From the Greek lasios (woolly) and akis (point), referring to the ‘fruit’ (mature floret).

Including Pseudolasiacis A. Camus

Habit, vegetative morphology. Perennial; rhizomatous to stoloniferous, or decumbent. Culms woody and persistent (usually), or herbaceous (10%); scandent (to 10 m in some species), or not scandent; self-supporting; sparsely to amply branched above, or unbranched above. The branching suffrutescent, or simple. Culm nodes glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; auriculate (with sheath auricles), or non-auriculate. Sheath margins free. Leaf blades linear to elliptic; broad; cordate, or not cordate, not sagittate; pseudopetiolate, or not pseudopetiolate; without cross venation; disarticulating from the sheaths; rolled in bud. Ligule an unfringed membrane to a fringed membrane; 0.1–9 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence paniculate (with the spikelets borne obliquely on their pedicels); open, or contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets morphologically ‘conventional’ (usually), or unconventional (L. anomala, with an extra sterile lemma); 2.6–5 mm long; slightly compressed dorsiventrally (subglobose); falling with the glumes; with conventional internode spacings, or with distinctly elongated rachilla internodes between the florets (in the form of a conical boss, in L. grisebachii and L. ruscifolia). Rachilla prolonged beyond the uppermost female-fertile floret (occasionally), or terminated by a female-fertile floret; the rachilla extension when present, naked. Hairy callus absent.

Glumes two; relatively large; very unequal; (the upper) about equalling the spikelets; (the upper) long relative to the adjacent lemmas; hairy (with webby white hairs at the apex); pointed, or not pointed; awnless; non-carinate; similar (membranous, abruptly apiculate, blackening and accumulating oil when mature). Lower glume 5–13 nerved. Upper glume 7–15 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1, or 2 (in L. anomala); paleate. Palea of the proximal incomplete florets not becoming conspicuously hardened and enlarged laterally. The proximal incomplete florets male, or sterile. The proximal lemmas apically pubescent, blackening and accumulating oil like the glumes; awnless; 7–15 nerved; more or less equalling the female-fertile lemmas (and the upper glume); less firm than the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas with a shallow excavation and a tuft of hair at the tip; decidedly firmer than the glumes; smooth; becoming indurated; usually turning dark brown in fruit; entire; blunt; awnless; hairy (with webby white hairs at the apex); non-carinate; having the margins inrolled against the palea; with a clear germination flap; 7 nerved. Palea present; relatively long; indurated; 2-nerved; 2-keeled (apically excavated, like the lemma). Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous; without a conspicuous apical appendage. Styles fused (basally), or free to their bases. Stigmas 2; white, or red pigmented.

Fruit, embryo and seedling. Fruit small; ellipsoid; broadly longitudinally grooved, or not grooved; compressed dorsiventrally. Hilum short. Embryo large; not waisted. Endosperm hard. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

First seedling leaf with a well-developed lamina. The lamina broad; curved to supine.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones exhibiting many atypical long-cells to without typical long-cells (the long-cells relatively short). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 48–55.5 microns long; 6–6.6 microns wide at the septum. Microhair total length/width at septum 7.6–9.3. Microhair apical cells 16.5–22.5 microns long. Microhair apical cell/total length ratio 0.34–0.47. Stomata common; 30–33 microns long. Subsidiaries triangular. Guard-cells overlapped by the interstomatals (e.g. L. sorghoides), or overlapping to flush with the interstomatals (e.g. L. procerrima). Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; with adaxial palisade; Isachne-type. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only, or having a conventional arc of bundles. Bulliforms present in discrete, regular adaxial groups (these broad, between main bundles); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Special diagnostic feature. Plants not as in Dichanthelium (q.v.).

Cytology. Chromosome base number, x = 9. 2n = 18 and 36.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Boivinellinae. 20 species.

Distribution, phytogeography, ecology. Tropical and subtropical America.

Mesophytic. Forest margins.

Rusts and smuts. Rusts — Physopella and Puccinia.

References, etc. Morphological/taxonomic: Parodi 1938; Davidse 1978. Leaf anatomical: studied by us - L. ligulata Hitchc. & Chase, L. nigra Davidse, L. procerrima Hitchc. ex Chase, L. sorghoides Hitchc. & Chase.

Illustrations. • L. divaricata, as Panicum: Kunth (1835). • L. divaricata: Hitchcock and Chase (1950). • Cordate leaf blade base (L. sorghiodes). • Germination flap of L. procerrima: Johnston and Watson (1981). Lasiacis procerrima. Double-convex flap.

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.’.