| # The grass genera of the world |

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

### Yvesia A. Camus

Named for M.A. Saint-Yves, French agrostologist.

Habit, vegetative morphology. Slender annual. The flowering culms leafless. Culms 15–22 cm high; herbaceous; unbranched above. Culm nodes exposed; glabrous. Leaves mostly basal (almost rosette-forming); non-auriculate. Sheaths glabrous, striate. Leaf blades lanceolate to ovate-lanceolate; narrow (but relatively broad); 2–4 mm wide; ‘basi rotundata’; flat (rigid, sub-erect); without cross venation; persistent. Ligule a fringed membrane; short. Contra-ligule absent.

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

Inflorescence. Inflorescence paniculate (delicate); open; with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund to not secund (the branches indistinctly unilateral); shortly to long pedicellate. Pedicel apices cupuliform.

Female-fertile spikelets. Spikelets about 2.5 mm long; lanceolate; adaxial (insofar as orientation detectable); slightly compressed dorsiventrally; biconvex; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. The callus hairs white (long, dense, to about 0.5 mm long). Callus blunt.

Glumes one per spikelet; (the upper, only glume) about equalling the spikelets; long relative to the adjacent lemmas; conspicuously hairy (with long, white pubescence); pointed (acute); awnless; non-carinate. Upper glume 3 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 conspicuously pubescent, similar to the glume; awnless; 5 nerved (the laterals inconspicuous); decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas obovate-oblong; decidedly firmer than the glumes (becoming cartilaginous, distinctly hardened); striate; entire; mucronate (or at least, mucronulate); hairless; glabrous; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved; with the nerves confluent towards the tip. Palea present; relatively long; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma (and glabrous); not indurated; 2-nerved; keel-less. Palea back glabrous. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea (but enclosed); small (1.2 mm long); yellow; not noticeably compressed; glabrous. Hilum short. Embryo large; waisted. Endosperm hard.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (fairly thin walled). Intercostal zones with typical long-cells, or exhibiting many atypical long-cells (often short to almost isodiametric). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls and having straight or only gently undulating walls. Microhairs present; panicoid-type (only the bases seen). Stomata common. Subsidiaries non-papillate; low dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells fairly common; in cork/silica-cell pairs; silicified. Intercostal silica bodies cross-shaped and oryzoid-type. No microhairs or prickles seen. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; ‘panicoid-type’; cross shaped, butterfly shaped, dumb-bell shaped, and nodular.

Transverse section of leaf blade, physiology. C4; XyMS+. PCR sheath outlines even. PCR sheath extensions absent. PCR cell chloroplasts seemingly centripetal (fairly clearly so, in the poorish material seen). Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (their median cells quite large and deeply penetrating, separating all the bundles). Many of the smallest vascular bundles unaccompanied by sclerenchyma (or with very little, some seemingly with none). Combined sclerenchyma girders present; forming ‘figures’ (the sclerenchyma quite scanty, forming slight I’s with larger bundles). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Melinidinae. 1 species (Y. madagascariensis).

Distribution, phytogeography, ecology. Madagascar.

Streamside rocks.

References, etc. Morphological/taxonomic: Camus 1927. Bull. Soc. Bot. Fr. 73, 687–690. Leaf anatomical: studied by us.

Illustrations. • Yvesia madagascariensis: Vorontsova & Rakotoarisoa (2014). • Abaxial epidermis of leaf blade of Y. madagascariensis: this project. • TS leaf blade of Yvesia madagascariensis: 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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