Family: Alismataceae
Arrowhead
Dennis Albert
Key to Wisconsin Sagittaria
Author: Christopher D. Tyrrell
- 1a. Lower, carpellate flowers sessile or, if pedicellate, pedicels evidently thickened: either at least half as thick as the main axis of the inflorescence or distinctly thicker than the pedicels of the staminate flowers 2
- 1b. Lower, carpellate flowers pedicellate, pedicels less than half the diameter of the main axis of the inflorescence (often much thinner), and not distinctly thicker than the pedicels of the staminate flowers 3
- 2a. Lower flowers ± long-pedicellate, pedicels of staminate flowers subequally as thick as those of the carpellate flowers; filaments longer than anthers; sepals of mature, carpellate flowers tightly appressed to or enclosing the fruiting head S. montevidensis
- 2b. Lower flowers sessile or very short-pedicellate, if present, those of the carpellate flowers thicker than those of the staminate flowers; filaments shorter than anthers; sepals of mature, carpellate flowers spreading to reflexed, or only appressed to base of fruiting head but not enclosing it S. rigida
- 3a. Filaments glabrous; emersed leaf blades with distinct basal lobes present, sagittate or hastate 4
- 3b. Filaments with scales or flattened hair; emersed leaf blades lacking distinct basal lobes, bases attenuate, rounded, truncate or only slightly cordate 6
- 4a. Tips of achene beaks pointing perpendicular to the long axis of the achene body, beaks arising laterally or obliquely, beaks usually greater than 0.4 mm long S. latifolia
- 4b. Tips of achene beaks pointing more or less parallel with the long axis of the achene body, beaks arising from or near to the apex, beaks 0.2–0.7 mm long 5
- 5a. Beak of achene minute, 0.2–0.3 mm long, apically attached but definitely set in from the margin S. cuneata
- 5b. Beak of achene 0.4–0.7 mm long, laterally or obliquely attached, appearing as a continuation of the margin of the achene, straight or curved outward or over apex of achene S. brevirostra
- 6a. Beak of achene 0.4–0.6 mm long; anthers clearly shorter than the filaments S. cristata
- 6b. Beak of achene minute, ca. 0.2 mm long; anthers as long as or longer than the filaments S. graminea
Vegetative morphology can vary greatly in some species, thus having mature fruits ensure the most accurate species identifications. The introduced species Peltandra virginica (L.) Schott (Araceae) can superficially resemble hastate- or sagittate-leaved members of Sagittaria when vegetative. The leaves of Peltandra, however, are glossy and have linear lateral veins arising from the mid-vein (vs. a dull sheen and arcuate lateral venation in Sagittaria). The presence or absence of corms and achene resin glands (referred to as “ducts” in some literature) can be instructive for separating similar species.
