How do sweet peas pollinate?

By Chelsie Vandaveer

January 15, 2003

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There are an estimated one hundred species in the genus Lathyrus--the sweet peas, grasspeas, and vetches. The plants are legumes and related to the edible garden pea (Pisum sativum) and the beans (Phaseolus spp. and Glycine max). But Lathyrus are seldom eaten since at least nine of the species are known to contain toxic amino acids.

Pinching out Heads of Sweet Peas to Encourage Bushy Growth
Mark Bolton Buy Photographic Print at AllPosters.com

Lathyrus are often native to dry or arid habitats. The genus has both perennial (lives several years) and annual (one year) species. Bees are the usual pollinator for Lathyrus. N. Ben Brahim, D. Combes, and M. Marrakchi studied the pollination of Lathyrus. They experimented with the flowers having bees excluded (bagged), open with stamens intact (receiving their own pollen by the bee), and open with stamens removed (receiving another flower's pollen).

Ben Brahim, Combes, and Marrakchi discovered that the perennial species would not produce seeds without a pollinator, but annual species like the sweet pea (Lathyrus odoratus) and grasspea (L. sativus) did produce a few pods with viable seeds. All of the species they examined produced many seeds when pollinators transferred the flower's own pollen to the stigma.

If the stamens were removed and the flowers could only get pollen from other flowers via the pollinator, seed production dropped, often to zero. Two of the wild perennial species produced a few seed pods. Three annual species produced a few pods with seeds.

Lathyrus odoratus (Sweet Pea), Annual Climber Photographic Print
Michele Lamontagne Buy Photographic Print at AllPosters.com

These three annual species (L. odoratus, L. sativus, and L. cicera) are the only three that self-pollinate without an insect pollinator and self- and cross-pollinate with the aid of a pollinator. They are also the only three that humans regularly cultivate. ("Autogamy and allogamy in genus Lathyrus", Ben Brahim, Combes, and Marrakchi, Lathyrus, Lathyrism Newsletter 2, 2001)

The National Sweet Pea Society, of the UK has posted information and photographs of the sweet pea, the best known of the cultivated Lathyrus. To view the photographs, click on the link and then click on the site link to its Gallery:

http://www.sweetpeas.org.uk/

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