Herbs, annual or perennial, unarmed, trichomes unicellular and eglandular, and/or multicellular and glandular; from rhizomes (rarely tuberous), rootstock, or taproots. Stems erect, sprawling, or climbing, angled and/or winged, glabrous or pubescent. Leaves alternate, even-pinnate (phyllodic in L. nissolia); stipules present, foliose, base usually semisagittate, rarely sagittate or hastate; rachis sometimes winged, usually terminated in simple or branched, prehensile tendril, sometimes reduced to bristle or absent; petiolate; leaflets (0 or)2–18, paired or unpaired, usually decreasing in size distally, stipels absent, blades 5–150 mm, margins entire, usually with several longitudinal veins in addition to midrib, surfaces glabrous or sparsely to densely pubescent. Inflorescences 1–20-flowered, axillary (terminal in L. pusillus), racemes or flowers solitary, erect or lax; bracts absent; bracteoles absent. Flowers papilionaceous; calyx symmetric or obliquely campanulate, without gibbous base, 5–12 mm, lobes 5, equal or unequal, when unequal, abaxial lobes short and triangular, lateral and keel lobes longer and lanceolate or linear; corolla white, cream, yellow, pink, lavender, lilac, rose, red, reddish orange, crimson, blue to purple, violet, magenta, or bicolored, wings and keel often lighter than banner, 6–30 mm; petal clawed, distinct from blade; stamens 10, diadelphous; anthers dorsifixed, uniform; style abaxially compressed, sometimes twisted, laterally pubescent. Fruits legumes, usually sessile, rarely stipitate, flattened or terete, linear, dehiscent, non-septate, usually with obscure margins, splitting along both margins, glabrous or sparsely pubescent; valves twisted after dehiscence. Seeds 3–15, usually dull brown, black, tan, or dark green, often mottled, spherical, sometimes angular. x = 7 (polyploidy rare).

Distribution

North America, Mexico, South America, Europe, Asia, n Africa, introduced widely in temperate regions.

Discussion

Species ca. 150 (41 in the flora).

F. K. Kupicha (1983) separated Lathyrus into 13 sections worldwide; about three-fourths of the members are perennials and one-fourth are annuals. All perennial North American species are included in sect. Orobus (Linnaeus) Godron, which contains about one-third of all Lathyrus species. The single native annual species, L. pusillus, has been assigned to sect. Notolathyrus Kupicha, a section perhaps closely allied to Orobus species in North America (C. B. Amussen and A. Liston 1998). Lathyrus is predominantly diploid with 2n = 14. Chromosome counts have been reported for 20 of the 29 species native to North America (S. L. Broich 1989). There has been no worldwide treatment of the genus at the species level. Lathyrus in North America was last revised by C. L. Hitchcock (1952) and summarized by D. Isely (1998).

Recent phylogenetic studies have placed Lathyrus consistently within the Vicieae (M. F. Wojciechowski et al. 2004); subgeneric relationships have yet to be resolved (C. B. Amussen and A. Liston 1998; G. J. Kenicer et al. 2005; H. Schaefer et al. 2012).

Twelve of the 41 Lathyrus species treated herein have been introduced to North America and have become locally established to widely naturalized. Deliberate introductions include species used as ornamentals, cover, and green manure and cover crops. One native species, L. pusillus, has been developed as a winter cover crop; a second native species, L. splendens, has been cultivated as an ornamental.

A number of native Lathyrus are polymorphic and include one or more of the following: glabrous and pubescent races, variation in stature and habit from short-stemmed and erect to long-stemmed and sprawling or climbing, variation in tendril morphology from bristles to well developed and branched, variable leaflet number, ovate and linear leafleted races, and variation in flower color and size. Within some polymorphic species, morphological variation is such that distinct varieties can be delimited. Within other species, however distinctive some populations may be, intergradation among forms is such that well-marked taxa cannot be reliably described.

Although probably cultivated where possible in North America and occasionally escaping, Lathyrus sativus Linnaeus and L. niger (Linnaeus) Bernhardi are not treated here.

Diets that include large quantities of flour made from seed of several Lathyrus species (primarily L. sativus, L. cicera Linnaeus, and L. clymenum Linnaeus) are known to produce lathyrism, a paralytic syndrome in humans and livestock (A. D. Kaul and D. Combes 1986). In humans, lathyrism has been associated historically with poverty or drought that force populations to rely on Lathyrus seed for consumption.

Unless otherwise noted in the taxon description: stipules are semisagittate; leaf rachises are not winged; styles are flattened perpendicular to the ovary axis and not rotated; legumes are sessile, without winged abaxial sutures, and are not prominently veined; vestiture, if reported present, consists of unicellular, eglandular trichomes; the number of leaflets and tendril morphology are for distal stem leaves bearing inflorescences; leaflet dimensions given are for basal leaflets on the rachis of leaves subtending inflorescences; flower lengths reported are the distance from the base of the calyx tube to the distal keel petal margin; references to the relationship between calyx lobe length and calyx tube length always take into account the longest lobe present; wing and keel petals are almost always lighter in color than the banner petal and colors given in descriptions are for the most pigmented part of the corolla. Distributions of introduced species are approximate.

Selected References

None.

Lower Taxa

Lathyrus angulatus, Lathyrus aphaca, Lathyrus biflorus, Lathyrus brachycalyx, Lathyrus brownii, Lathyrus cicera, Lathyrus decaphyllus, Lathyrus delnorticus, Lathyrus eucosmus, Lathyrus glandulosus, Lathyrus graminifolius, Lathyrus grimesii, Lathyrus hirsutus, Lathyrus hitchcockianus, Lathyrus holochlorus, Lathyrus japonicus, Lathyrus jepsonii, Lathyrus laetivirens, Lathyrus lanszwertii, Lathyrus latifolius, Lathyrus littoralis, Lathyrus nevadensis, Lathyrus nissolia, Lathyrus ochroleucus, Lathyrus odoratus, Lathyrus palustris, Lathyrus pauciflorus, Lathyrus polyphyllus, Lathyrus pratensis, Lathyrus pusillus, Lathyrus rigidus, Lathyrus sphaericus, Lathyrus splendens, Lathyrus sulphureus, Lathyrus sylvestris, Lathyrus tingitanus, Lathyrus torreyi, Lathyrus tracyi, Lathyrus tuberosus, Lathyrus venosus, Lathyrus vestitus

Key

1	Leaflets 0 or 2.	> 2
2	Leaflets 0.	> 3
3	Stipules ovate, base hastate; leaf rachises reduced to branched or unbranched tendrils; corollas yellow.	Lathyrus aphaca
3	Stipules filiform-linear, base semisagittate; tendrils absent, leaves phyllodic, grasslike; corollas crimson.	Lathyrus nissolia
2	Leaflets 2.	> 4
4	Herbs perennial; inflorescences 4–15-flowered.	> 5
5	Corollas yellow.	Lathyrus pratensis
5	Corollas reddish, purple, magenta, pink, or white.	> 6
6	Stems not winged; ovaries glabrous.	Lathyrus tuberosus
6	Stems broadly winged; ovaries glandular-pubescent.	> 7
7	Stipules 7–15 mm wide, at least 1/2 width of stem.	Lathyrus latifolius
7	Stipules 1–3 mm wide, less than 1/2 width of stem.	Lathyrus sylvestris
4	Herbs annual; inflorescences 1–3(or 4)-flowered.	> 8
8	Stems not winged; inflorescences extending beyond terminal flower in a bristle.	> 9
9	Inflorescences 2–7 cm; legumes with indistinct reticulate venation.	Lathyrus angulatus
9	Inflorescences 1–2 cm; legumes with prominent longitudinal venation.	Lathyrus sphaericus
8	Stems narrowly to broadly winged; inflorescences with a terminal flower.	> 10
10	Ovaries densely pustulose-based pubescent.	> 11
11	Flowers 20–25 mm.	Lathyrus odoratus
11	Flowers 8–10 mm.	Lathyrus hirsutus
10	Ovaries glabrous.	> 12
12	Leaf rachis not winged; flowers 7–10 mm.	Lathyrus pusillus
12	Leaf rachis winged (as the stem); flowers 10–30 mm.	> 13
13	Flowers 20–30 mm; lateral calyx lobes deltate, usually shorter than tube.	Lathyrus tingitanus
13	Flowers 10–12 mm; lateral calyx lobes linear-triangular, much longer than tube.	Lathyrus cicera
1	Leaflets (2–)4–18.	> 14
14	Tendrils often absent or reduced to bristles, not well developed.	> 15
15	Leaflet blades obovate to oblanceolate, surfaces densely villous; corollas dark purple; coastal sand dunes, deflation plains along Pacific Coast from c California northward to British Columbia.	Lathyrus littoralis
15	Leaflet blades usually linear, lanceolate, or ovate, rarely obovate, surfaces not densely villous; corollas blue-purple, lilac, pinkish, violet, magenta, or cream to white; not coastal.	> 16
16	Corollas white or cream.	> 17
17	Inflorescences 5–15-flowered; n California.	Lathyrus tracyi
17	Inflorescences 1–6-flowered; w North America.	> 18
18	Stipules much smaller than distal leaflets.	> 19
19	Flowers 7–15 mm; inflorescences 2–5 cm; Arizona, California, Colorado, Nevada, New Mexico, c Oregon, Utah, c Washington, Wyoming.	Lathyrus lanszwertii
19	Flowers 18–22 mm; inflorescences 3–15 cm; ne Oregon, se Washington, adjacent Idaho.	Lathyrus nevadensis
18	Stipules equal to distal leaflets.	> 20
20	Flowers 7–8 mm; leaflet blades finely villous; Humboldt County, California.	Lathyrus biflorus
20	Flowers 12–18 mm; leaflet blades glabrous; California, Nevada, Oregon, adjacent Idaho.	Lathyrus rigidus
16	Corollas usually blue-purple, sometimes violet to magenta, lavender, or pinkish.	> 21
21	Flowers 8–12 mm.	> 22
22	Leaflets 2–4, blades 20–50 mm; British Columbia, n Idaho, w Montana, e Washington.	Lathyrus lanszwertii
22	Leaflets 8–16, blades 5–15 mm; coastal forests of California, Oregon, Washington.	Lathyrus torreyi
21	Flowers 13–20 mm.	> 23
23	Leaflets usually scattered; legumes sessile.	> 24
24	Leaflets 6–12; n Arizona, sw Colorado, s Idaho, Nevada, nw New Mexico, Utah.	Lathyrus brachycalyx
24	Leaflets 4 or 6; n California, Oregon, Washington.	Lathyrus nevadensis
23	Leaflets usually paired; legumes stipitate.	> 25
25	Leaflets 8–12; flowers 16–22 mm; Great Plains and e slopes of Rocky Mountains.	Lathyrus decaphyllus
25	Leaflets 4–8; flowers 12–18 mm; California, Idaho, Nevada, Oregon.	> 26
26	Stipules much smaller than distal leaflets; Elko County, Nevada.	Lathyrus grimesii
26	Stipules equal to distal leaflets; e Oregon, adjacent w Idaho, ne California, nw Nevada.	Lathyrus rigidus
14	Tendrils well developed, often branched.	> 27
27	Stipules sagittate; lake and ocean shores in North America, ca. 38–70o N latitude.	Lathyrus japonicus
27	Stipules semisagittate; not of coastal shores, sometimes coastal wetlands.	> 28
28	Corollas usually white, cream-white, or yellow-cream, rarely light pink or lavender.	> 29
29	Corollas orange to yellow-cream, banner blade shorter than claw; California Central Valley and adjacent foothills, northward to sw Oregon.	Lathyrus sulphureus
29	Corollas white or cream-white (sometimes light pink or lavender in L. laetivirens); banner blade equal to or longer than claw; distribution widespread.	> 30
30	Leaflets usually paired.	> 31
31	Leaflets (5 or)6(–8), stipules somewhat foliose, sometimes equal to distal leaflets; n North America (sw Alaska to Washington, eastward to Atlantic coast).	Lathyrus ochroleucus
31	Leaflets 4–10, stipules much smaller than leaflets; nw California southeastward to New Mexico.	> 32
32	Tendrils well developed, often branched; Arizona, Colorado, Nevada, New Mexico, Utah.	Lathyrus laetivirens
32	Tendrils 0–3 cm, usually not branched; n California.	Lathyrus tracyi
30	Leaflets usually scattered (paired in L. hitchcockianus, L. palustris).	> 33
33	Stems narrowly winged.	> 34
34	Stipules sometimes equal to distal leaflets; nw California, adjacent Oregon.	Lathyrus delnorticus
34	Stipules much smaller than distal leaflets; w California, Oregon, Washington.	> 35
35	Lateral calyx lobes lanceolate, (wider distal to base); stems basally branched; coastal ranges of n California, w Oregon, Washington.	Lathyrus vestitus
35	Lateral calyx lobes linear-triangular; stems often branched mid stem (at or just proximal to flowering nodes); Willamette Valley, Oregon, Washington.	Lathyrus holochlorus
33	Stems angled but not winged.	> 36
36	Inflorescences 2–6-flowered; Colorado, Utah, Wyoming.	Lathyrus lanszwertii
36	Inflorescences (2–)5–20-flowered; Arizona, California, Idaho, New Mexico, Oregon, Texas, Washington.	> 37
37	Lateral calyx lobes lanceolate (wider distal to base); coastal ranges of n California, Oregon, Washington.	Lathyrus vestitus
37	Lateral calyx lobes deltate or linear-triangular; Arizona, Idaho, New Mexico, Oregon, Texas, Washington.	> 38
38	Leaflet blades usually linear, rarely lanceolate; Arizona, New Mexico, w Texas.	Lathyrus graminifolius
38	Leaflet blades ovate to lanceolate; Idaho, Oregon, Washington.	> 39
39	Stems branched from base or unbranched; Idaho.	Lathyrus nevadensis
39	Stems often branched mid stem (at or just proximal to flowering nodes); Oregon, Washington.	Lathyrus holochlorus
28	Corollas pink, lavender, rose, blue to purple, or deep red.	> 40
40	Stems narrowly to broadly winged.	> 41
41	Leaflets 14–18, blade surfaces: both with eglandular trichomes, glandular-pubescent abaxially; Humboldt and n Mendocino counties, California.	Lathyrus glandulosus
41	Leaflets 4–12, blade surfaces glabrous, glabrate, or eglandular-pubescent; ne North America, coastal marshes along Pacific Coast of Oregon northward, or coastal mountains of w California from Humboldt County southward to Monterey County.	> 42
42	Leaflets 4–8, paired; ovaries glandular-pubescent; ne, e, midwestern North America and coastal marshes along Pacific Coast from California northward.	Lathyrus palustris
42	Leaflets 8–12, scattered; ovaries glabrous; c, n California from Monterey County northward to Humboldt County eastward through Central Valley.	Lathyrus jepsonii
40	Stems angled but not winged.	> 43
43	Leaflets 4 or 6, paired; flowers 8–10 mm; Grapevine Mountains of Inyo County, California and adjacent Nye County, Nevada.	Lathyrus hitchcockianus
43	Leaflets (2–)6–16, scattered; flowers (7–)10–30 mm; distribution widespread.	> 44
44	Flowers 16–30 mm, corollas deep wine red, banners reflexed toward calyx tube; sw California.	> 45
45	Flowers 16–25 mm.	Lathyrus vestitus
45	Flowers 25–30 mm.	Lathyrus splendens
44	Flowers (7–)10–20(–25) mm, corollas lavender, pink, or blue to purple, banners erect; distribution widespread.	> 46
46	Leaflets 10–16; stipules nearly equal to distal leaflets.	Lathyrus polyphyllus
46	Leaflets 4–10(–14); stipules much smaller than leaflets.	> 47
47	Wings longer than keel (by 1–4 mm).	> 48
48	Inflorescences 3–4 cm, 2–4-flowered; ne California, adjacent Nevada and Oregon.	Lathyrus brownii
48	Inflorescences 5–18 cm, 4–13-flowered; sw Colorado, Idaho, ne Oregon, Utah, e Washington.	Lathyrus pauciflorus
47	Wings equal to keel.	> 49
49	Corollas white to blue-orchid; leaflet blades usually linear, rarely lanceolate; stems sometimes branched at flowering nodes; inflorescences 10–18 cm; Arizona, New Mexico, w Texas.	Lathyrus graminifolius
49	Corollas rose, lavender, or blue-purple; leaflet blades usually ovate to lanceolate or elliptic, rarely linear; stems usually basally branched; inflorescences 2–10(–25) cm; distribution widespread.	> 50
50	Legumes short-stipitate; inflorescences 2–4-flowered; flowers 18–20 mm; Arizona, Colorado, New Mexico, w Texas, se Utah, Wyoming.	Lathyrus eucosmus
50	Legumes sessile; inflorescences 2–20-flowered; flowers (7–)10–18(–20) mm; distribution north and west or eastern United States.	> 51
51	Inflorescences 5–20-flowered.	> 52
52	Stipules of distal leaves usually less than 1/4 width of distal leaflets; central and eastern North America.	Lathyrus venosus
52	Stipules on distal leaves usually more than 1/4 width of distal leaflets; coastal mountains of California into sw Oregon.	Lathyrus vestitus
51	Inflorescences 2–6-flowered.	> 53
53	Banner deeply cordate; n Arizona, sw Colorado, e Nevada, nw New Mexico, w, se Utah.	Lathyrus brachycalyx
53	Banner retuse to shallowly cordate; coastal ranges of California, northward to British Columbia, Great Basin.	> 54
54	Flowers 10–15 mm; leaflet blades usually lanceolate, rarely linear; ne California, w Nevada, c Idaho, e Oregon, ne Utah, se Washington.	Lathyrus lanszwertii
54	Flowers 13–18 mm; leaflet blades ovate to lanceolate; coastal ranges of California northward to British Columbia.	Lathyrus nevadensis