| The Families of Angiosperms |
L. Watson and M.J.Dallwitz
~Araceae
IncludingWolffiaceae (Engl.) Nak.
Habit and leaf form.Much reduced, aquaticherbs.Plants ofvery peculiar vegetative form;thalloid (thallus small to minute,globular, flat or linear, with one (Wolffioideae) or two (Lemnoïdeae)budding pouches, raphides present with mucilage cells in Lemnoïdeae only,xylem without vesses, phloem transfer cells lacking at least inLemna).Leavesabsent. Plants with roots (usually, inLemnoïdeae), or rootless (Wolffioïdeae). Annual. Hydrophytic; freefloating.
Axial (stem, wood) anatomy.Secondary thickening absent.
Root anatomy.Root xylem withoutvessels.
Reproductive type, pollination.Unisexual flowers present. Plants monoecious (usually), or dioecious(rarely).
Inflorescence, floral, fruit and seedmorphology.Flowers aggregated in ‘inflorescences’ (ingroups of 2—3, these developed in one of the budding pouches inLemnoïdeae but from a dorsal cavity in Woffioïdeae). Inflorescencesspatheate (Lemnoïdeae), or espatheate (Wolffioïdeae). Flowers minute.
Perianth absent.
Androecium1; exclusively of fertile stamens.Stamens1. Anthers dehiscing transversely (Lemnoïdeae), ordehiscing via pores to dehiscing via longitudinal slits (Wolffioïdeae);unilocular (Wolffioïdeae), or bilocular (Lemnoïdeae); bisporangiate(Wolffia), or tetrasporangiate (Lemna). Endothecium developingfibrous thickenings. The endothecial thickenings spiral. Microsporogenesissuccessive. The initial microspore tetrads tetrahedral, or isobilateral. Antherwall 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.Gynoeciumostensiblymonomerous (imaginatively interpretable aspseudomonomerous?);ostensiblyof one carpel; superior. Carpel1–7 ovuled.Placentationbasal. Ovules ascending;orthotropous, or anatropous, or hemianatropous; bitegmic; crassinucellate. Outerintegument contributing to the micropyle, or not contributing to the micropyle.Embryo-sac developmentPolygonum-type, orAllium-type. Polarnuclei fusing prior to fertilization. Antipodal cells formed; 3; notproliferating; ephemeral, or persistent (Spirodela). Synergidspear-shaped. Endosperm formation cellular. Endosperm haustoria present;chalazal. Embryogeny onagrad (or irregular).
Fruit non-fleshy. The fruiting carpel indehiscent; a 1—4-seededutricle. 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 withoutphytomelan; thick.
Seedling.Seedling collar notconspicuous. Coleoptile absent. Seedling cataphylls absent. Primary rootephemeral (absent).
Physiology, phytochemistry.C3. C3 physiology recordeddirectly inLemna.Anatomynon-C4 type(Lemna,Spirodela). Accumulated starch exclusively‘pteridophyte type’. Not cyanogenic. Alkaloids absent (one species).Arbutin absent. Proanthocyanidins absent. Flavonols absent. Ellagic acid absent.
Geography, cytology.Frigid zoneto tropical. Cosmopolitan.X = 5, 8, 10, 11, 21. Supposed basicchromosome number of family: 5 (?).
Taxonomy.SubclassMonocotyledonae. Dahlgrenet al. Superorder Ariflorae; Arales. APG IIIcore angiosperms; Superorder Lilianae; non-commelinid Monocot. APG IV OrderAlismatales (as a synonym ofAraceae).
Species 30. Genera 4–6; Lemnoïodeae:Lemna,Spirodela (includingLandoltia); Wolffioïdeae:Pseudowolffia,Wolffia,Wolffiella,Wolffiopsis.
General remarks.The data compiledfor the present descriptions suggest that these genera, comprising two ratherdistinct subfamilies (see above) and credibly interpreted as derived fromAraceae, are inappropriately sunk therein by dogmatic application ofcladistic hypotheses.
Economic uses, etc.Besides beinga likely future source of clean biofuel, Duckweeds have an important rôlein removing excess nutrients and other pollutants from artificial and naturallyoccurring bodies of water.
Quotations.
. . . The greenmantle of the stagnant pool
(‘King Lear’, iii., 4 -Lemnaminor)
Illustrations.• Le Maout and Decaisne: Lemna. • Le Maout and Decaisne: Wolffia (including Grantia,Telmatophace). • Lemna gibba:Eng. Bot. 1396 (1869). • Lemnaminor: Eng. Bot. 1395 (1869). • Lemna polyrrhiza: Eng. Bot. 1397 (1869).• Lemna trisulca: Eng. Bot. 1394(1869). • Wolffia arrhiza: asLemna, Eng. Bot. 1398 (1869).
We advise against extracting comparative informationfrom the descriptions. This is much more easily achieved using theDELTA data files or theinteractive key, which allows access to the characterlist, illustrations, full and partial descriptions, diagnostic descriptions,differences and similarities between taxa, lists of taxa exhibiting or lackingspecified 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). See alsoGuidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., andDallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions,illustrations, identification, and information retrieval. Version: 25th March2025.delta-intkey.com’.
