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Jepson Interchange (more information)
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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. foliosus Raf.

LEAFY PONDWEED

Perennial, from densely matted, slender rhizomes
Stem many-branched, somewhat flattened
Leaves all submersed, 1–10 cm, < 0.3 cm wide, linear; veins < 7; stipules fused, sheath-like
Inflorescence subspheric to short spike, < 1 cm; peduncle club-shaped
Fruit: back keeled; sides rounded to slightly concave
Ecology: Shallow water, ponds, lakes, streams, irrigation ditches
Elevation: < 2300 m.
Bioregional distribution: California (except Cascade Range Foothills, c&s High Sierra Nevada, Channel Islands)
Distribution outside California: to Alaska, e Canada, C.America

Native

var. fibrillosus (Fernald) R.R. Haynes & Reveal

FIBROUS PONDWEED


Stem < 60 cm
Leaf 2–4 cm, 1–2 mm wide; base generally with 2 glands; tip acute; stipules < 12 cm, persistent, clearly veined, becoming fibrous
Inflorescence head-like or short spike, interrupted; peduncle 4–12 mm
Fruit 1.4–1.7 mm, 1.1–1.2 mm wide, pale green; back with keel < 0.2 mm high; beak ± 0.2 mm
Ecology: Shallow water, small streams
Elevation: < 1300 m.
Bioregional distribution: n North Coast (Crescent City), w Modoc Plateau, s East of Sierra Nevada
Distribution outside California: to Washington, Idaho, Wyoming
See the CNPS Inventory for information about endangerment and rarity.
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