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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. epihydrus Raf. subsp. nuttallii (Cham. & Schldl.) Calder & Roy L. Taylor

NUTTALL'S PONDWEED

Perennial from slender, matted rhizomes
Stem simple or few-branched, < 170 cm, somewhat flattened
Leaves: submersed leaves sessile, 5–25 cm, 0.2–1 cm wide, linear, ribbon-like, with median strip clearly net-like, tip acute; floating leaves generally opposite, petiole long, flattened, blade 2–8 cm, 0.4–3.5 cm wide, generally oblong to elliptic, tapered to petiole, tip rounded; stipules generally < 4 cm, fused, not sheathing, ligule-like
Inflorescence: spike, 1–4 cm
Fruit 2–4 mm, spheric to obovate; back 3-keeled; sides concave
Chromosomes: n=13
Ecology: Shallow water, ponds, lakes, streams, irrigation ditches
Elevation: 400–1900 m.
Bioregional distribution: Outer North Coast Ranges, High Sierra Nevada, Modoc Plateau
Distribution outside California: to Alaska, e N.America, Colorado
Ssp. epihydrus in e North America. Hybridizes with P. nodosus.
See the CNPS Inventory for information about endangerment and rarity.
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