Lathyrus

1. Leaflets mostly 4–12 (in depauperate plants, some leaves with only 2 leaflets); native species.

2. Stipules (at least the larger ones, on upper part of plant) (7–) 10–20 (–25) mm broad; larger leaflets (1.2–) 1.5–3 (–3.5) cm wide; stems angled but not winged.

3. Flowers (except in rare albinos) purple to blue (or pinkish); stipules with 2 basal lobes (± hastate); sandy shores, beaches, and dunes.

L. japonicus

3. Flowers cream; stipules with 1 basal lobe (semi-sagittate or semi-cordate); thickets and forests.

L. ochroleucus

2. Stipules all less than 7 mm broad (very rarely broader, usually on plants with winged stems); larger leaflets 0.4–2.4 cm wide; stems winged or not.

4. Calyx glabrous or sparsely pubescent; principal leaves with 4–6 (–10) leaflets; racemes 2–8-flowered; stems often narrowly winged.

L. palustris

4. Calyx (and usually to some extent other parts) ± densely pubescent; principal leaves with 8–12 (–14) leaflets; racemes 6–26-flowered; stem not winged.

L. venosus

1. Leaflets 2; plants escaped from cultivation, usually near settlements or along roadsides.

5. Stems not winged (at most angled); flowers ca. 11–19 mm long.

6. Stipules (at least on main stem) with 2 basal lobes (hastate or sagittate); flowers bright yellow; leaflets narrowly acute at the tip.

L. pratensis

6. Stipules with 1 basal lobe (semi-sagittate); flowers rose-red; leaflets broadly acute to rounded at the tip (except for excurrent midvein).

L. tuberosus

5. Stems distinctly winged with strips of green leaf-like tissue; flowers of various size.

7. Ovary and fruit pubescent with pustular-based hairs; annual.

8. Flowers less than 1.5 cm long; leaflets linear-lanceolate.

L. hirsutus

8. Flowers over 2 cm long; leaflets elliptic.

L. odoratus

7. Ovary and fruit glabrous; perennials.

9. Main lobe of stipules more than half as wide as the winged stem; flowers ca. 16–26 mm long.

L. latifolius

9. Main lobe of stipules up to half as wide as the winged stem; flowers ca. 12–18 mm long.

L. sylvestris

All species found in Lathyrus

Lathyrus hirsutusWILD PEA 
Lathyrus japonicusBEACH PEA 
Lathyrus latifoliusPERENNIAL PEA, EVERLASTING PEA 
Lathyrus ochroleucusPALE VETCHLING 
Lathyrus odoratusSWEET PEA 
Lathyrus palustrisMARSH PEA 
Lathyrus pratensisYELLOW VETCHLING 
Lathyrus sylvestrisPERENNIAL PEA, EVERLASTING PEA 
Lathyrus tuberosusTUBEROUS VETCHLING 
Lathyrus venosusVEINY PEA 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. September 23, 2017. http://michiganflora.net/genus.aspx?id=Lathyrus.