| # The grass genera of the world |

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

### Hydrochloa P. Beauv.

From the Greek hudor (water) and chloa (grass), alluding to habitat.

~ Luziola (L. fluitans, = H. caroliensis

Habit, vegetative morphology. Perennial; a slender aquatic, floating or with trailing culms 30–100 cm long. Culms herbaceous; branched above. Leaves not basally aggregated; with auricular setae (usually 2 or 3 on either side). Leaf blades narrow; 2–5 mm wide (by 2–6 cm long); flat. Ligule an unfringed membrane; 0.5–1 mm long.

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 and male-only. The male and female-fertile spikelets in different inflorescences (male spikelets in small few-flowered terminal panicles or racemes, female spikelets axillary, solitary or in few-flowered racemes). The spikelets overtly heteromorphic.

Inflorescence. Inflorescence reduced to a single spikelet, or few spikeleted; a single raceme, or paniculate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent.

Female-sterile spikelets. Male spikelets about 4 mm long, 1-flowered, the lemma thin and 7-nerved the palea thin and 2-nerved, the floret with 6 free stamens. The male spikelets without glumes; 1 floreted. Male florets 6 staminate. The staminal filaments free.

Female-fertile spikelets. Spikelets unconventional (through lacking organs, presumably glumes); 2 mm long; not noticeably compressed to compressed dorsiventrally; abscising below the spikelet. Rachilla terminated by a female-fertile floret.

Glumes absent. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas not becoming indurated (thin); entire; pointed; hairless; without a germination flap; 5–7 nerved. Palea present; relatively long (thin); not indurated; several nerved (4–7); one-keeled. Stamens 0. Styles fused (?). Stigmas 2 (long).

Fruit, embryo and seedling. Pericarp fused.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal. Intercostal papillae complex - one large papilla on each long-cell and interstomatal, itself covered by the numerous, minute papillae which extend over most of the cell surface. Long-cells markedly different in shape costally and intercostally (the costals much narrower and more regular); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells irregular, but rectangular; having markedly sinuous walls. Microhairs present (detectable by the bases, but hard to locate and none seen in good condition); ostensibly one-celled (cf. Luziola?); minute. Stomata fairly common (in single files near the costal zones); 18–21 microns long. Subsidiaries often papillate (two papillae each, near their ends). Guard-cells deeply sunken amongst the surrounding papillate cells. Intercostal short-cells common; silicified. Intercostal silica bodies oryzoid-type. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; exclusively dumb-bell shaped (short).

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade; probably with arm cells (but the material seen very poor); without fusoids. Midrib fairly conspicuous (by its larger bundle); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (a large group in each intercostal zone); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 12. 2n = 24.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Oryzeae. Soreng et al. (2015): Oryzoideae; Oryzeae; Zizaniinae. 1 species (H. caroliniensis).

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

Hydrophytic.

References, etc. Leaf anatomical: studied by us.

Special comments. Fruit data wanting.

Illustrations. • Hydrochloa caroliniensis: P. Beauv. (1812).

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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