| # The grass genera of the world |

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

### Leucopoa Griseb.

~ Festuca

Including Hesperochloa Rydb., Xanthochloa

Habit, vegetative morphology. Perennial; rhizomatous, or caespitose. Culms 30–120 cm high; herbaceous. Culm internodes hollow. Leaves non-auriculate. Leaf blades narrow; flat; not pseudopetiolate; without cross venation. Ligule an unfringed membrane; truncate; 0.1–5 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets, or dioecious (sporadically); with hermaphrodite florets (usually), or without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or female-only, or male-only.

Inflorescence. Inflorescence paniculate; open, or contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 6–10 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; pointed, or not pointed; awnless; carinate; similar. Lower glume 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.

Female-fertile florets 3–9. Lemmas less firm than the glumes; not becoming indurated; entire to incised (irregularly serrate); not deeply cleft; awnless; hairless; carinate to non-carinate; without a germination flap; 5 nerved. Palea present; relatively long; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 3. Anthers 2.5–4.5 mm long. Ovary apically hairy. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit not grooved. Hilum long-linear. Embryo small. Endosperm hard; containing compound starch grains. Embryo with an epiblast.

First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular (mostly), or fusiform (a few); having markedly sinuous walls (thick and pitted). Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; in cork/silica-cell pairs (but the ‘silica cells’ without silica); not silicified. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies rounded (mostly), or crescentic (some); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only, or having a conventional arc of bundles (minor bundles flanking midrib). Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 7. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Loliinae. 6 species.

Distribution, phytogeography, ecology. Western & Central Asia to Himalayas, North America.

References, etc. Leaf anatomical: studied by us - L. spadicea (= Festuca paniculata?).

Special comments. Leucopoa is probably a nonsense genus, to which assorted supposedly monoecious or dioecious species of ‘Festuca’ sensu lato have sometimes been referred. Anyway, if the name is to be retained, this description should be checked against direct observations on the morpholoy and anatomy of ‘L. carpatica (F. Dietr.) H. Scholtz’.

Illustrations. • Leucopoa albida (cf. Festuca sibirica?): Keng yi li (1957).

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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