| # The grass genera of the world |

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

### Ystia P. Compère

Named after Rd. Père Vanderyst (van der Yst), Belgian agrostologist.

~ Schizachyrium (S. kwiluense)

Habit, vegetative morphology. Perennial. Culms about 50–150 cm high; herbaceous; branched above. Leaves not basally aggregated. Leaf blades narrowly linear; narrow; without cross venation. Ligule an unfringed membrane; short.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality; overtly heteromorphic (the pedicellate spikelets with awns reduced or lacking).

Inflorescence. Inflorescence paniculate (a false panicle of small ‘racemes’); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’; the spikelet-bearing axes with 6–10 spikelet-bearing ‘articles’ (with 6–7 spikelet pairs); solitary (in the spatheoles); with very slender rachides (flexuose); disarticulating; disarticulating at the joints. ‘Articles’ scabrid. Spikelets paired and in triplets (with terminal triad); sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite.

Female-fertile spikelets. Spikelets 4–5 mm long; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; blunt.

Glumes present; two; long relative to the adjacent lemmas; hairless (glabrous below, scabrid above); awnless; very dissimilar (the G1 papery with involute margins and apically bidentate, the G2 thinner, naviculate, shortly subulate or acuminate). Lower glume not two-keeled (except at the tip); not pitted; relatively smooth; (5–)7(–9) nerved. 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 (reduced to a hyaline lemma); sterile. The proximal lemmas awnless.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; incised; deeply cleft (to about a third); awned (in the sessile spikelet), or awnless to mucronate (in the pedicellate spikelet). Awns 1; median; from a sinus; geniculate; shortly hairy, or hairless (scabrid); about as long as the body of the lemma to much longer than the body of the lemma (4–5 mm long, in the sessile spikelet). Lemmas non-carinate; without a germination flap. Palea absent. Lodicules present; 2; fleshy. Stamens 3. Stigmas 2.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae (as a synonym?); Andropogonodae; Andropogoneae; Andropogoninae. 1 species (Y. stagnina, cf. Schizachyrium kwiluense).

Distribution, phytogeography, ecology. Tropical Africa.

References, etc. Morphological/taxonomic: Compère 1963.

Special comments. Fruit data wanting. Anatomical data wanting.

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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