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The grass genera of the world

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

Psilolemma Phillips

Name alluding to smooth, glabrous lemmas.

Habit, vegetative morphology. Perennial; stoloniferous (a wiry mat-grass). Culms 7–35 cm high; herbaceous; sparsely branched above. The branching simple. Culms tuberous. Leaves not basally aggregated; conspicuously distichous; non-auriculate. Leaf blades linear (stiff, pungent); narrow; to 2 mm wide; rolled (convolute); without abaxial multicellular glands; without cross venation. Ligule a fringed membrane to a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence of spicate main branches (with few-spiculate racemes appressed to the central axis, the upper racemes often reduced to single spikelets), or paniculate (the lower racemes sometimes branched); contracted (spiciform); spicate; non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets pedicellate (the pedicels to 3 mm long).

Female-fertile spikelets. Spikelets 8–15 mm long; compressed laterally (slightly), or not noticeably compressed; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; awnless; non-carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets without proximal incomplete florets.

Female-fertile florets 4–14. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (membranous); not becoming indurated; entire; blunt; awnless; hairless; glabrous; non-carinate (abaxially rounded); 3 nerved. Palea present; relatively long (glabrous); awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Palea keels glabrous (smooth). Stigmas 2.

Fruit, embryo and seedling. Fruit small (1.1–1.2 mm long); ellipsoid; not noticeably compressed. Hilum short. Pericarp loosely adherent (removable when soaked). Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (or the costals rather narrower); differing markedly in wall thickness costally and intercostally (the costals thinner walled, and less conspicuously pitted). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 36.6–40.5 microns long. Microhair basal cells 27 microns long. Microhairs 18–21 microns wide at the septum. Microhair total length/width at septum 1.8–2. Microhair apical cells 12–16.5 microns long. Microhair apical cell/total length ratio 0.31–0.41. Stomata common; 22.5–33 microns long. Guard-cells overlapped by the interstomatals (conspicuously so, the entire stomatal apparatus sunken and the seemingly dome-shaped subsidiaries obscured). Intercostal short-cells common; in cork/silica-cell pairs and not paired (some solitary); silicified. Intercostal silica bodies imperfectly developed; rounded and oryzoid-type. Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; rounded to saddle shaped (intergrading); not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (round topped). Midrib with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (these large, in at least some of the furrows). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (all the bundles with large fibre groups, with girders or strands abaxially but seemingly only strands adaxially). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Zoysieae; Sporobolinae. 1 species (P. jaegeri).

Distribution, phytogeography, ecology. East Africa.

Species of open habitats; halophytic (coloniser of soda mud-flats).

References, etc. Morphological/taxonomic: Phillips 1973. 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.’.