The grass genera of the world
Type species: type: not designated. Lecto: X. imberbis R.Br. fide R.D.Webster, Austral. Paniceae 261 (1987).
Including Kerinozoma Steud.
Habit, vegetative morphology. Annual (rarely), or perennial; caespitose (often rush-like), or decumbent. Culms woody and persistent, or herbaceous. Culm nodes glabrous. Culm leaf sheaths rounded. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; setaceous, or not setaceous; flat, or rolled (involute); without cross venation; persistent. Ligule a fringed membrane (very reduced).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets, or without hermaphrodite florets (the upper floret of perfect spikelets sometimes (?) being female, with 2–3 staminodes). The spikelets of sexually distinct forms on the same plant (heteromorphous, with some of the spikelets reduced); hermaphrodite and sterile, or hermaphrodite, female-only, and sterile.
Inflorescence. Inflorescence of globose, spathaceous units, fascicled and interspersed with prophylls, the fascicled units solitary and terminating the culm, or arranged in a leafy panicle. Inflorescence axes not ending in spikelets (the rachis produced beyond the uppermost spikelet). Inflorescence spatheate; a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes very much reduced (to very short spikes, with tough rachides); clustered (with groups of 3–5 in a spathe); disarticulating; falling entire, or disarticulating at the joints (the ultimate units breaking up, or falling entire). Spikelets solitary; not secund; sessile; not in distinct long-and-short combinations.
Female-sterile spikelets. The literature suggests that some spikelets are variously reduced.
Female-fertile spikelets. Spikelets 4.8–12 mm long; oblong, or elliptic, or lanceolate, or ovate, or obovate; abaxial; compressed laterally to compressed dorsiventrally; falling with the glumes (with the spikelet bearing axes falling, and a second zone of disarticulation beneath the glumes); with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes one per spikelet, or two; very unequal; shorter than the adjacent lemmas; hairy, or hairless; awnless; non-carinate. Lower glume 0–1 nerved. Upper glume 2–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 3–9 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (membranous to cartilaginous, with a hyaline area at the base).
Female-fertile florets 1. Lemmas acuminate; decidedly firmer than the glumes (membranous to cartilaginous); smooth to rugose (or muricate); becoming indurated to not becoming indurated; white in fruit, or yellow in fruit, or brown in fruit; entire; awnless; hairless; glabrous; non-carinate; with a clear germination flap, or without a germination flap; 2 nerved. Palea present; convolute around the flower; textured like the lemma; 2-nerved. Lodicules absent (or vestigial). Stamens 3, or 0 (or staminodal?). Anthers not penicillate. Ovary apically glabrous. Styles fused. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Embryo large. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular, or fusiform; having markedly sinuous walls. Microhairs present (often arising from specialized epidermal cells); panicoid-type; (48–)51–72(–78) microns long; (10.5–)11.4–14.4(–15) microns wide at the septum. Microhair total length/width at septum 3.6–6.5. Microhair apical cells (27–)30–51(–57) microns long. Microhair apical cell/total length ratio 0.53–0.75. Stomata common; (30–)33–51 microns long. Subsidiaries dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs (usually); silicified. Costal zones with short-cells. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies rounded (predominating), or panicoid-type; not sharp-pointed.
Transverse section of leaf blade, physiology. Leaf blades almost entirely consisting of midrib (obviously so in X. barbata and X. imberbis, less obviously so in X. laniflora where the quite broad midrib is recognisable as such by the reduced lateral flanges and with reference the other species).
C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Midrib (i.e. the bulk of the blade) having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms not present in discrete, regular adaxial groups (the adaxial epidermis being largely bulliform); associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. Rush-like, with reduced leaf blades, or not rush-like.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 4 species.
Distribution, phytogeography, ecology. Siam, Java, Australia.
Xerophytic (extreme); species of open habitats. Dry stream beds and clay flats.
References, etc. Morphological/taxonomic: Webster 1987. Leaf anatomical: this project.
Illustrations. • X. barbata, X. laniflora: Gardner, 1952. • X. barbata, X. imberbis: Gardner, 1952. • Spatheate 'partial inflorescences' (X. lanifolia). • Spikelet close-up. • X. imberbis, abaxial epidermis of leaf blade: this project. • X. imberbis, T.S. of midrib-like leaf blade: 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: 13th November 2017. delta-intkey.com/grass’.