The families of flowering plants
Including Wolffiaceae (Engl.) Nak.
Habit and leaf form. Much reduced, aquatic herbs. Plants of very peculiar vegetative form; thalloid (thallus small to minute, globular, flat or linear, with or without raphides). Leaves absent. Plants with roots, or rootless. Annual. Hydrophytic; free floating.
General anatomy. Accumulated starch exclusively pteridophyte type.
Leaf anatomy. The mesophyll inapplicable, but the thallus contains mucilage cells. Minor leaf veins inapplicable, but the thallus of Lemna minor is without phloem transfer cells.
Stem anatomy. Secondary thickening absent. Xylem (thallus) without vessels.
Root anatomy. Root xylem without vessels.
Reproductive type, pollination. Plants monoecious (usually), or dioecious (rarely).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in inflorescences (in groups of 23). Inflorescences spatheate, or espatheate. Flowers minute.
Androecium 1; exclusively of fertile stamens. Stamens 1. Anthers dehiscing transversely, or dehiscing via pores to dehiscing via longitudinal slits (sometimes dehiscing apically via pores or short slits); bisporangiate (Wolffia), or tetrasporangiate (Lemna). Endothecium developing fibrous thickenings. The endothecial thickenings spiral. Microsporogenesis successive. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall with no middle layer; of the reduced type. Tapetum amoeboid. Pollen grains aperturate; 1 aperturate; ulcerate; 3-celled.
Gynoecium ostensibly 1 carpelled. The pistil 1 celled. Gynoecium ostensibly monomerous (imaginatively interpretable as pseudomonomerous?); ostensibly of one carpel; superior. Carpel 1–7 ovuled. Placentation basal. Ovules ascending; orthotropous, or anatropous, or hemianatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle, or not contributing to the micropyle. Embryo-sac development Polygonum-type, or Allium-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral, or persistent (Spirodela). Synergids pear-shaped. Endosperm formation cellular. Endosperm haustoria present; chalazal. Embryogeny onagrad (or irregular).
Fruit non-fleshy. The fruiting carpel indehiscent; a 14-seeded utricle. Seeds endospermic, or non-endospermic. Endosperm oily, or not oily. Seeds with starch. Embryo weakly differentiated to well differentiated (sometimes lacking a radicle). Cotyledons 1. Embryo straight. Testa without phytomelan; thick.
Seedling. Seedling collar not conspicuous. Coleoptile absent. Seedling cataphylls absent. Primary root ephemeral (absent).
Physiology, biochemistry. Not cyanogenic. Alkaloids absent (one species). Proanthocyanidins absent (as a synonym of Araceae). Flavonols absent. Ellagic acid absent. Arbutin absent. C3. C3 physiology recorded directly in Lemna. Anatomy non-C4 type (Lemna, Spirodela).
Geography, cytology. Frigid zone to tropical. Cosmopolitan. X = 5, 8, 10, 11, 21. Supposed basic chromosome number of family: 5 (?).
Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Ariflorae; Arales. APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order Alismatales.
Species 30. Genera 5; Lemna, Spirodela, Wolffia, Wolffiella, Wolffiopsis.
Illustrations. • Technical details: Lemna. • Technical details: Wolffia (including Grantia, Telmatophace). • Lemna gibba: Eng. Bot. 1396 (1869). • Lemna minor: Eng. Bot. 1395 (1869). • Lemna polyrrhiza: Eng. Bot. 1397 (1869). • Lemna trisulca: Eng. Bot. 1394 (1869). • Wolffia arrhiza: as Lemna, Eng. Bot. 1398 (1869).
. . . The green mantle
of the stagnant pool
(King Lear, iii., 4 - Lemna minor)
This description is offered for casual browsing only. We strongly advise against extracting comparative information from it. This is much more easily achieved using 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, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG).
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 19th December 2012. http://delta-intkey.com’.