Flora of North America species comparison

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Alismataceae

arrowhead family, water-plantain family
Habit Herbs, annual or perennial, rhizomatous, stoloniferous, or cormose, caulescent, glabrous to stellate-pubescent; sap milky.
Roots

septate or not septate.
Leaves

basal, submersed, floating, or emersed, sessile or petiolate, sheathing proximally;

blade with translucent markings of dots or lines present or absent, basal lobes present or absent;

venation reticulate, primary veins parallel from base of blade to apex, secondary veins reticulate.
Inflorescences

scapose racemes or panicles, rarely umbels, erect, rarely floating or decumbent, whorled (forming racemes) or whorls branching (forming panicles), bracteolate.
Flowers

bisexual or unisexual, if unisexual, staminate and pistillate on same or different plants, hypogynous, subsessile to long-pedicellate;

sepals persistent, 3;

petals deciduous, 3, delicate;

stamens 0, 6, 9, or to 30, distinct;

anthers 2-loculed, dehiscing longitudinally;

pistils 0 or 6–1500 or more, distinct or coherent proximally, 1-loculed;

placentation basal;

ovules1–2.
Fruits

achenes or follicles.
Seeds

embryo U-shaped;

endosperm absent in mature seed.

Alismataceae
Distribution
Nearly worldwide; primarily tropical and subtropical regions
[BONAP county map]
Discussion

Genera 12, species ca. 80 (4 genera, 34 species in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Pistils weakly coherent proximally into starlike aggregation; petals erose
Damasonium
1. Pistils distinct, forming heads or rings; petals entire.
→ 2
2. Pistils arranged in ring around margin of flattened receptacle.
Alisma
2. Pistils spirally arranged on convex receptacle.
→ 3
3. Flowers all bisexual; fruits mostly plump, longitudinally ribbed, lateral wings absent.
Echinodorus
3. Flowers unisexual (at least the proximal); fruits compressed, lateral wing often present, 1, curved.
Sagittaria
Source FNA vol. 22, p. 7. Authors: Robert R. Haynes, C. Barre Hellquist.
Parent taxa
Subordinate taxa
Alisma, Damasonium, Echinodorus, Sagittaria
Name authority Ventenat
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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