Lathyrus japonicus

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Name: Lathyrus japonicus Willd.

Family: Fabaceae (the pea family)

Common Names: Beach pea, Sea pea, Sand pea (1,13) 

Etymology: The original name Lathyros comes from a leguminous plant named by Theophrastus, from the prefix la, meaning “very” and thuros, meaning “passionate”. Japonicus simply means “of Japan” (3,5). 

Lmaritimus1_JdoreyBotanical synonyms: Lathyrus maritimus Bigelow (3,4), Pisum maritimum L. (3)

Quick Notable Features:
¬ Stipules with 2 basal lobes
¬ Mostly 4-12 leaflets
¬ Stems angled but not winged
¬ Tendrils are borne from the leaf tips

Plant Height: L. japonicus can grow to 1.5 meters in length (5).

Subspecies/varieties recognized:  According to ITIS (2) there are 5 recognized varieties

Lathyrus japonicus var. japonicus
Lathyrus japonicus var. maritimus
Lathyrus japonicus var. parviflorus
Lathyrus japonicus var. pellitus
Lathyrus japonicus var. pubescens 

Most Likely Confused with: Other species of Lathyrus, including L. ochroleucus, L. venosus, and L. palustris as well as Wisteria floribunda, W. frutescens, and W. sinensis. 

Habitat Preference: L. japonicus can be found on dunes, sandy to gravelly beaches, and adjacent to disturbed ground along large bodies of water (4). 

Geographic Distribution in Michigan: L. japonicus has been witnessed in both the upper and lower peninsulas of Michigan, all of which border the Great Lakes with the exception of Crawford County (1).

Known Elevational Distribution: L. japonicus grows to 300m above sea level (9).

Complete Geographic Distribution: L. japonicus is native to North America. It is found in all of the Great Lakes States, as well as in every state from New Jersey north to Maine, and every state on the West Coast. It is found in every Canadian province and territory except Alberta and Saskatchewan. It is also found in Chile (1,6).

Lmaritimus2_JdoreyVegetative Plant Description: L. japonicus has a compound leaf with between 4 and 12 firm leaflets but has been seen with as few as 2. The leaflets are approximately 1.5-3 cm wide and 1-7 cm long. The stipules are between 10-25 mm wide and have hastate lobes. The petioles are slightly bristly above. The stems are erect, semi-woody, and angled, sprawling, or flanged. The tendrils can be found coiled, branched, or neither and are borne from the leaf tips. This species is highly variable (4,5,6,14).

Climbing Mechanism:  Tendrils are borne on the leaf tips (13).

Flower Description: L. japonicus has 3-10 fragrant purple to bluish flowers that are occasionally white. The flowers are borne in a raceme and are 1.2-3.0 cm long. The flowers are “papilionate” (14) or butterfly like, meaning that there is a banner petal, two wing petals, and a keel petal. The corolla is 1.8-2.2 cm. The peduncles are filiform and 0.7-2.5 cm wide. There are 10 stamens that are separated into 2 bundles of 1 and 9. The styles are bent nearly at a right angle to the ovary. The ovary is puberulent (4,5,14).

lathyrusjapo_frFlowering Time: In the Pacific Northwest, L. japonicus flowers from May to September and from June to late August in Britain (9,13).

Pollinator: Bees pollinate the flowers, as evidenced by their color and scent (9).

Fruit Type and Description: The fruit is a legume about 3-7 cm long that is firm and has a paper like texture. It is also puberulent (5,6,7).

Seed Description: The seeds are 1 to 8 mm in length and when fresh are pale green. The seeds have a hard seed coat that prevents germination until scarification – this usually occurs as the seeds scrape on gravel and sand when washed on to the shore (10).

laja_001_lhpDispersal Syndrome: L. japonicus seeds are dispersed primarily by water and they have been found to be viable even after floating for as much as 5 years in seawater.  They have also been found in the crops of birds, which suggests that its breadth of distribution may be due to long-distance dispersal by birds (8,10).

Distinguished by: L. japonicus can be distinguished from L. ochroleucus by the cream flowers of L. ochroleucus. The stipules only have 1 basal lobe whereas L. japonicus has 2 lobes. Additionally, L. ochroleucus is often found in thickets and woodlands as opposed to beaches.  L. japonicus can be distinguished from both L. venosus and L. palustris via its broad stipules: those of L. japonicus are 10-20 mm broad as opposed to only 7 mm wide for L. venosus and L. palustris. The calyx of L. venosus is densely pubescent and L. japonicus is not, and the stems of L. palustris are often winged while L. japonicus has angled stems. L. japonicus can be distinguished from any Wisteria speies by its tendrils borne on the ends of the leaves (4,5). 

Other members of the family in Michigan: There are 9 species of Lathyrus in Michigan and a total of 36 different varieties between those 9 species. Other genera found in Michigan are Amorpha, Amphicarpaea, Anthyllis, Apios, Astragalus, Baptisia, Caragana, Cercis, Chamaecrista, Cladrastis, Colutea, Crotalaria, Cytisus, Dalea, Desmodium, Genista, Gleditsia, Glycine, Gymnocladus, Hedysarum, Kummerowia, Lespedeza, Lotus, Lupinus, Melilotus, Mimosa, Orbexilum, Phaseolus, Pisum, Pueraria, Robinia, Securigera, Senna, Strophostyles, Tephrosia, Trifolium, Vicia, Vigna, and Wisteria (1).

Ethnobotanical Uses: The seeds and the leaves both are edible. However, the seeds contain a toxin that is the source of lathyrism, a disease affecting the nervous system. Lathyrism arises when the seed is consumed in very large quantities (approximately 30% of daily caloric intake). If it is consumed in smaller quantities it is both safe and nutritious (8).

FABALathyrusjaponicusMAPPhylogenetic Information: Lathyrus, within the Fabaceae, belongs to the subfamily Papilionoideae (Faboideae). The Fabaceae is a member of the order Fabales. Fabales are a member of the Eurosids I clade. They form a monophyletic group with Zygophyllales, Celastrales, Malpighiales, Oxalidales, Rosales (including Urticales), Cucurbitales, Fagales. Fabales are dicots (11,12).

Interesting Quotation or Other Interesting Factoid not inserted above: The plant was rumored to be an aphrodisiac, hence the original name (5).

Literature and websites used:

  1. USDA, NRCS. 2008. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490 USA.  (10-17-08)
  2. ITIS: Integrated Taxonomic Information System Last Modified: 1-8-08 (10-17-08)
  3. Robert W. Freckmann Herbarium University of Wisconsin-Stevens Point. Last modified: March 19, 2008 (10-19-08)
  4. Voss, E.G. 1985. Michigan Flora Part II: Dicots. Ann Arbor, Michigan, USA: Cranbrook Institute of Science.
  5. Fernald, M.L. 1950. Gray’s Manual of Botany, 8th ed. New York, USA: American Book Company.
  6. Hickman, J.C. 1993. The Jepson Manual. Berkley and Los Angeles, California, USA: University of California Press.
  7. Hitchcock, C.L. & A. Cronquist 1973. Flora of the Pacific Northwest. Seattle, Washington: University of Washington Press.
  8. Plants For A Future, 1996-2003. Last modified: June 2004. (12-10-08)
  9. Hill, S. 2006. Re-introduction of Lathyrus japonicus at Elliot Links SSSI in Angus: ecological and management aspects. Scottish Natural Heritage Commissioned Report No. 200.
  10. Chinnasamy, G. & A.K. Bal 2003. The pattern of seed development and maturation in beach pea (Lathyrus maritimus). NRC Research Press.
  11. Solomon, J. 2006. W3TROPICOS VAST nomenclatural database. Missouri Botanical Garden. (12-10-08)
  12. Judd, W.S., C.S. Campbell, E.A. Kellogg & P.F. Stevens 1999. Plant Systematics: A Phylogenetic Approach.  Sunderland, Massachusetts, USA: Sinauer Associates, Inc.
  13. Adams, M.J. 2006. Washington State University Island County Beach Watchers. Last modified: August 22, 2006 ( (2-3-08)
  14. Brightmore, D. & P.H.F. White. 1963. Lathyrus japonicus Willd. Journal of Ecology 51(3): 795-801.

Image Credits (all used with permission):
1) Image of flowers and leaves in beach habitat taken by Jenna Dorey, copyright JD.
2) Image of flowers and young fruits taken by Jenna Dorey, copyright JD.
3) Image of L. japonicus seeds taken by Steve Hurst and retrieved from the U. S. Department of Agriculture via the USDA PLANTS Website
4) Image of the legume fruits taken by Janet Novak of the Connecticut Botanical Society.
5) Species distribution map, derived from the Michigan Flora Online.

Primary Authors: Bradley Sisson with edits from John Bradtke and Robyn J. Burnham, and images from Jenna Dorey.

© Robyn J. Burnham, University of Michigan

For additional information on Michigan Plant Diversity species accounts, please contact Robyn J. Burnham via email: rburnham“at”