Jepson Flora Project: Jepson Interchange    

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Jepson Interchange (more information)
©Copyright 1993 by the Regents of the University of California

  • Up-to-date information about California vascular plants is available from the Jepson eFlora.



Wayne P. Armstrong

Perennial, floating aquatics, small, clonal, in dense populations; new plants produced in budding pouch at base or along margins; may overwinter on bottom as dense, rootless, starch-filled daughter plant (winter bud); roots 0–many
Plant body 0.4–10 mm, flat and tongue-shaped to spheric
Flower 1, rarely seen, minute, appearing like 2–3 unisexual flowers, often sheathed by minute membrane; perianth 0; stamens 1–2; pistil 1, simple, maturing before stamens
Fruit achene-like, sometimes winged
Seeds 1–3, smooth or ribbed. Spp. best separated by chemistry and fruit; clones vary; magnification, backlighting generally needed to identify vegetative plants
Genera in family: 4 genera, 34 species: worldwide; ornamental in pools, aquaria
Reference: [Landolt 1986 Veröff Geobot Inst ETH Stiftung Rübel Zürich 71]
Horticultural information: TRY.



Plants generally in unequal pairs; roots 0
Plant body 0.4–1.3 mm, nearly spheric to ± cylindric, floating on or partially below water surface; veins 0; budding pouch funnel-shaped; winter buds often produced
Flower produced in cavity on upper surface; sheathing membrane 0; stamen 1; pistil 1
Seed smooth
Species in genus: 9 species: worldwide, especially temp, tropical
Etymology: (J.F. Wolff, German botanist and physician, 1778–1806)
Reference: [Armstrong & Thorne 1984 Madroño 31:172–179]
CA species may be distinguished by size and shape with > 10X magnification.


W. arrhiza (L.) Wimm.

Plant body 0.8–1.3 mm, nearly spheric; upper surface distinctly flattened, with 15–100 stomates, dark green (transparent below), only central portion floating above water
Ecology: Uncommon. Freshwater
Elevation: < 200 m.
Bioregional distribution: South Coast (San Diego Co.)
Distribution outside California: to Europe, sw Asia, Africa
In backlight, plants appear slightly darker than other transparent green species. Easily confused with W. columbiana.

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