The Families of Flowering Plants

L. Watson and M. J. Dallwitz


Hydatellaceae Hamann

~ Centrolepidaceae

Habit and leaf form. Aquatic herbs. Glabrous annual; with a basal aggregation of leaves (the stems very short). Hydrophytic to helophytic; rooted. Leaves submerged and emergent. Leaves alternate; spiral; sub- terete, or flat; sessile; sheathing. Leaf sheaths not tubular; with free margins. Leaves simple; epulvinate. Lamina entire; linear; one-veined, or parallel-veined. Leaves eligulate; presumably with a persistent basal meristem, and basipetal development.

General anatomy. Plants without silica bodies.

Leaf anatomy. Stomata present; anomocytic.

Lamina internally centric. The mesophyll not containing mucilage cells; without calcium oxalate crystals. Vessels present (Wagner 1977); end-walls scalariform.

Stem anatomy. Secondary thickening absent. Xylem with vessels. Vessel end-walls scalariform.

Root anatomy. Root xylem with vessels. Vessel end-walls scalariform.

Reproductive type, pollination. Plants monoecious (the heads mixed in Trithuria, mostly unisexual in Hydatella). Floral nectaries absent (nectaries lacking). Autogamous or pollinated by water.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in heads; more or less in ‘spikelets’. Inflorescences usually more or less scapiflorous; terminal; with involucral bracts; pseudanthial. Flowers bracteate; ebracteolate; small; 1 merous. Hypogynous disk absent.

Perianth absent.

Androecium 1 (i.e. the male flower consisting of a single stamen); exclusively of fertile stamens. Stamens 1. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; bilocular; tetrasporangiate. Microsporogenesis successive. Pollen grains aperturate; 1 aperturate; sulcate. Interapertural interstitium columellate.

Gynoecium ostensibly 1 carpelled. The pistil 1 celled. Gynoecium monomerous, or syncarpous (perhaps pseudomonomerous, depending on interpretation); of one carpel, or eu-syncarpous (?); superior. Carpel 1 ovuled. Placentation apical. Ovary 1 locular; shortly stipitate. Gynoecium non-stylate (if a tuft of filamentous structures represents stigmas), or stylate (if it is stylar). Styles 3–10 (if so interpreted); free; apical. Stigmas 3–10 (if the filamentous structures be are so interpreted). Placentation apical. Ovules non-arillate; anatropous; bitegmic; crassinucellate to pseudocrassinucellate. Endosperm formation cellular (sic).

Fruit non-fleshy. The fruiting carpel (if considered monomeric) dehiscent, or indehiscent; a follicle (?), or an achene (Hydatella). Fruit if considered syncarpous dehiscent, or indehiscent; a capsule, or achene-like (?). Capsules three valvular (Trithuria). Seeds ‘almost’ non-endospermic. Perisperm present (starchy). Seeds with starch. Embryo rudimentary at the time of seed release. Testa operculate; without phytomelan (?).

Geography, cytology. Western Australia, New Zealand.

Taxonomy. Subclass Monocotyledonae. Superorder Commeliniflorae; Hydatellales. APG (1998) Monocot; Commelinoid group; Poales. Species 3. Genera 2; Hydatella, Trithuria.


Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. http://biodiversity.uno.edu/delta/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).

Index