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	©Copyright 1993 by the Regents of the University of California Print edition is available from the University of California Press

	The second edition of The Jepson Manual (2012) is available from the University of California Press
	See also the Jepson eFlora, which parallels the Second Edition

POTAMOGETONACEAE

PONDWEED FAMILY

Robert F. Thorne

Annual, perennial herb, aquatic, (generally fresh to alkaline water), glabrous, from rhizomes or small, bulb-like, winter buds
Stems erect, simple to branched, cylindric or flattened
Leaves simple, cauline, alternate or in subopposite pairs; submersed thread-like to round, sessile or petioled; floating, if present, elliptic to ovate, petioled, leathery; sheath open, continuous with petiole or ± free from leaf base, generally with stipules, stipules sometimes fused, ligule-like
Inflorescence: spike or head-like, axillary or terminal, generally emergent, peduncled; bracts 0
Flower bisexual; perianth parts 0 or 4, clawed; stamens 2 or 4, if 4, each fused to base of perianth part, sessile or filament short, wide, anthers open to outside; pistils 4, ovary 1-chambered, ovule 1, style short or stigmas sessile
Fruit: drupe
Seed 1
Genera in family: 3 genera, ± 95 species: worldwide
Recent taxonomic note: Recently treated to include Zannichelliaceae [Angiosperm Phylogeny Group 1998 Ann Missouri Bot Gard 85:531–553].

POTAMOGETON

PONDWEED

Annual, perennial herb, from rhizomes or small, bulb-like, winter buds
Stem simple or branched, cylindric or flattened, rooting at lower nodes
Leaves simple, cauline, generally alternate, generally flat, generally green, margin generally entire; submersed leaves sessile or petioled, linear to round, tip rounded to acuminate, veins 1–35; floating leaves, if any, elliptic to ovate, generally petioled, leathery; stipules free or fused, sheath-like below leaf junction, free or fused (ligule-like) above leaf junction
Inflorescence: cylindric spike or head-like, axillary or terminal, floating to emergent
Flower: inconspicuous; perianth parts 4, clawed, greenish; stamens 4, attached to base of perianth, anthers generally sessile; ovule attached at chamber base, style short or stigma sessile
Fruit generally obovate, sessile, floating
Species in genus: ± 90 species: mostly temp n hemisphere
Etymology: (Greek: river neighbor, from aquatic habitat)
Reference: [Haynes 1974 Rhodora 76:564–649; 1985 Sida 11:173–188; Wieglet 1988 Feddes Repert 99:249–266]

Native

P. diversifolius Raf.

DIVERSE-LEAVED PONDWEED

Perennial, delicate
Stem much-branched above, < 50 cm, cylindric
Leaves: submersed leaves sessile, < 6 cm, < 0.5 cm, linear, thin, tip acute, stipules < 1 cm, fused to blade, sheath-like below, ligule-like above; floating leaves with petiole < 2 X blade, blade 0.5–3 cm, 0.3–0.8 mm wide, elliptic, tapered at both ends, stipules < 2 cm, fused to leaf, not sheathing, ± ligule-like
Inflorescence < 1.5 cm; lowermost spheric, submersed, subsessile; upper spike-like, emergent, peduncled
Fruit 1.1–1.8 mm, subspheric, 3-keeled, compressed, with 2 low, lateral keels; back with 1 wavy or fine-toothed keel; sides flattened to concave
Ecology: Uncommon. Shallow water, ditches, ponds, lakes
Elevation: < 2500 m.
Bioregional distribution: Inner North Coast Ranges, c Sierra Nevada Foothills, n High Sierra Nevada, Great Central Valley, South Coast, San Jacinto Mountains, Modoc Plateau
Distribution outside California: to British Columbia, e US, Arizona, Mexico
Horticultural information: fresh water, SUN: 1, 2, 3, 4, 5, 6, 7, 8, 9, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24.