| # The grass genera of the world |

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

### Triplasis P. Beauv.

From the Greek triplasios (triple), alluding to lemmas with an awn and two subulate lobes.

Including Diplocea Raf., Merisachne Steud., Uralepis Nutt

Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 30–100 cm high; herbaceous; unbranched above. Culm nodes hairy. Leaves not basally aggregated; non-auriculate (but with hair tufts at the auricle regions). Leaf blades narrow; flat, or rolled (involute); without abaxial multicellular glands; without cross venation; rolled in bud. Ligule a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous; with hidden cleistogenes. The hidden cleistogenes in the leaf sheaths (the culms breaking at the nodes, leaving the cleistogenes within the sheaths; small panicles in upper sheaths, reduced to modified spikelets in the lower ones).

Inflorescence. Inflorescence few spikeleted; paniculate (short, purple); open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 6–10 mm long; linear; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with a distinctly elongated rachilla internode above the glumes and with distinctly elongated rachilla internodes between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus present.

Glumes two; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; pointed, or not pointed; awnless; carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets.

Female-fertile florets 2–4. Lemmas incised; 2 lobed; mucronate, or awned. Awns when present, 1; from a sinus (or mucronate from the notch); non-geniculate; hairy (silky tomentose); much shorter than the body of the lemma to about as long as the body of the lemma (to slightly longer). Lemmas hairy (the nerves silky-villous); carinate; without a germination flap; 3 nerved. Palea present; 2-nerved; 2-keeled. Palea keels hairy (densely long-villous, glabrous between them). Lodicules present; 2; fleshy. Ovary apically glabrous. Styles fused. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small; dull brown; ellipsoid. Pericarp thin; fused (?). Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (the intercostal zones in deep grooves). Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells, or exhibiting many atypical long-cells (with short members, in places). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type (but the apical cells unusually thin walled, often collapsed). Microhair apical cell wall thinner than that of the basal cell and often collapsed to thinner than that of the basal cell but not tending to collapse. Microhairs of T. pupurea 24–27 microns long. Microhair basal cells 30 microns long. Microhairs 11.4–13.5 microns wide at the septum. Microhair total length/width at septum 1.9–2.3. Microhair apical cells 5.4–8.4 microns long. Microhair apical cell/total length ratio 0.2–0.3. Stomata common (in deep grooves, overarched by the costal prickles); 16.5–27 microns long. Subsidiaries low dome-shaped (predominating), or triangular. Guard-cells overlapped by the interstomatals to overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (sometimes paired with prickles, sometimes ostensibly solitary). Intercostal silica bodies absent. Large costal and small intercostal prickles abundant. Costal zones with short-cells. Costal short-cells conspicuously in long rows, or conspicuously in long rows, predominantly paired, and neither distinctly grouped into long rows nor predominantly paired (i.e. varying from place to place in T. americana). Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; large, dumb-bell shaped (short to long); 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 both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal (in T. americana). Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size (round to flat topped). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in every furrow); associated with colourless mesophyll cells to form deeply-penetrating fans (these continued into the colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (every bundle with a conspicuous I or ‘anchor’). Sclerenchyma all associated with vascular bundles. The lamina margins without fibres.

Special diagnostic feature. Spikelets without a terminal clavate appendage.

Cytology. Chromosome base number, x = 10.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Gouiniinae. 2 species.

Distribution, phytogeography, ecology. Southeast U.S.A.

Xerophytic; species of open habitats. Dry sandy soils.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia schedonnardi. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: studied by us - T. americana Beauv., T. purpurea (Walt.) Chapm.

Special comments. Fruit data wanting.

Illustrations. • Triplasis americana: P. Beauv. (1812). • Triplasis purpurea (as Uralepis): Kunth (1835). • T. purpurea: Hitchcock and Chase (1950). • Triplasis purpurea, abaxial epidermis of 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: 15th June 2025. delta-intkey.com’.

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