The Genus Lathyrus
Outwardly, some of the vetches, (genus Vicia) may resemble the members of the genus Lathyrus. With the latter, a good diagnostic feature would be to look at the style which will be flattened with hairs on one side while with vetch flowers, the style will be needle-like but with a ring of hairs about 1 mm wide all around the tip.
Yellow Vetchling, Yellow Pea: Lathyrus aphaca - Annual. Leaflets lacking, the stipules being large and leaf-like. Flowers single, yellowish, 10-14 mm long.
Everlasting Pea, Everlasting-pea, Perennial Peavine: Lathyrus latifolius (Synonym: Synonym: Lathyrus latifolius var. splendens) - Perennial. Leaves with 2 leaflets. Prehensile tendrils present. Stems stout, climbing, winged or with flattened margins. Racemes 5-15 flowered, pink to rose in color.
Sierran Peavine: Lathyrus nevadensis var. pilosellus - Perennial. Leaves with 4 or more leaflets. Prehensile tendrils lacking or moderately developed (as with this variety). Racemes 2-5 flowered. Flowers bluish to reddish-purple, typically less than 17 mm long.
Few-flowered Pea: Lathyrus pauciflorus var. pauciflorus - Perennial. Leaves with 4-10 leaflets. Prehensile tendrils present. Stipules shorter than to 1/2 the leaflet length. Keel usually 2-4 mm shorter than the wing petals. Racemes 3-7 flowered. Flowers whitish, lavender or purple, usually at least 18 mm long.
Leafy Pea: Lathyrus polyphyllus - Perennial. Leaves with 10-16 leaflets. Prehensile tendrils present. Stipules generally at least 1/2 the leaflet length. Racemes 5-12 flowered.
Grass Pea, Grass Peavine: Lathyrus sphaericus - Annual. Leaves with 2 leaflets. Flowers single, bluish to bluish-purple or reddish-purple.
Torrey's Pea: Lathyrus torreyi - Perennial. Leaves with 4 or more leaflets. Prehensile tendrils lacking. Racemes only 2-flowered.