| # The grass genera of the world |

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

### Euchlaena Schrad.

From the Greek eu (well) and chlaina (cloak), re the well covered (husked) fruiting spikes.

~ Zea

Habit, vegetative morphology. Robust annual, or perennial. Culms 200–500 cm high; herbaceous; unbranched above. Culm internodes solid. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades broadly linear-lanceolate; broad; 20–80 mm wide; flat; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane. Contra-ligule absent.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only, or male-only. The male and female-fertile spikelets in different inflorescences. The spikelets overtly heteromorphic.

Inflorescence. Inflorescence comprising terminal panicles of male spikelets, and axillary spikes of pistillate spikelets. Rachides of female inflorescence hollowed. Inflorescence spatheate. Spikelet-bearing axes spikes (female, these borne two to several, enclosed in foliaceous spathes or husks, in the leaf sheaths), or ‘racemes’ (male); (the females) with substantial rachides; disarticulating (i.e., the female rachides); disarticulating at the joints. ‘Articles’ non-linear; without a basal callus-knob; not appendaged; disarticulating obliquely; somewhat hairy, or glabrous. Spikelets solitary (females), or paired (males); secund (male pairs on one side of the rachis), or not secund (females); biseriate (the male pairs), or distichous (female); sessile (female), or sessile and pedicellate (the males in sessile-pedicellate pairs); consistently in ‘long-and-short’ combinations (male), or not in distinct ‘long-and-short’ combinations (female).

Female-sterile spikelets. Male inflorescence and spikelets like those of Zea. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes (two, many nerved); without proximal incomplete florets; 2 floreted. The lemmas awnless. Male florets 2; 3 staminate.

Female-fertile spikelets. Spikelets abaxial (the G1 covering the rachis cavity); compressed laterally; falling with the glumes (and with the joint). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; glabrous; apiculate; awnless; non-carinate; very dissimilar (G1 indurate, G2 membranous). Lower glume not two-keeled; convex on the back; not pitted; relatively smooth; about 11–13 nerved. Upper glume 9 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 awnless; 2 nerved, or 3 nerved; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; awnless; hairless; non-carinate; without a germination flap; 1 nerved. Palea present; relatively long; apically notched; textured like the lemma (hyaline); not indurated; 2-nerved; keel-less. Lodicules absent. Stamens 0. Ovary apically glabrous. Styles fused (nearly to the tip). Stigmas 2.

Fruit, embryo and seedling. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls (thin). Microhairs present; panicoid-type (but the distal cells rather inflated); 60–72 microns long. Microhair apical cells 36–48 microns long. Microhair apical cell/total length ratio 0.64. Stomata common. Subsidiaries triangular. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies cross-shaped, tall-and-narrow, and vertically elongated-nodular. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (E. mexicana); XyMS–. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with non-radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (a large median, flanked on either side by a large lateral and smaller bundles of various sizes); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans (the cells large). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the larger bundles). Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Fruiting inflorescence not as in maize (q.v.) (the female spikelets free of one another, falling, not forming a cob).

Cytology. Chromosome base number, x = 10. 2n = 20 and 40. 2 and 4 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Maydeae. Soreng et al. (2015): Panicoideae (? - as a synonym of Zea); Andropogonodae; Andropogoneae; Tripsacinae. 4 species.

Distribution, phytogeography, ecology. Mexico.

Mesophytic. Field margins.

Economic aspects. Cultivated fodder: E. mexicana (Teosinte).

Hybrids. Intergeneric hybrids with Zea - ×Euchlaezea Janaki ex Bor.

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

References, etc. Leaf anatomical: Metcalfe 1960.

Special comments. The descriptions of maize relatives require updating, to conform with modern taxonomic views (e.g. Doebley and Iltis 1980, Iltis 1987). The older and convenient but artificial treatment, separating the readily distinguishable Zea mays from the rest, is retained here pending acqisition of detailed comparative morphological data.

Illustrations. • Euchlaena luxurians: Bot. Mag. 105 (1879). • Euchlaena mexicana: Hitchcock and Chase (1950). • Grass pollen antigens: Watson and Knox (1976).

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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