The Sweet Pea (Lathyrus odoratus) is the flower of the month for April. The sweet pea is popularly known as the "Queen of Annuals". The name "sweet pea" is believed to have first been used by the poet Keats (1795-1821). The Latin name for the sweet pea is Lathyrus odoratus. This was the name chosen by the great Swedish naturalist Linnaeus to replace the former, less memorable, but highly descriptive Lathyrus distoplatyphyllus, hirsutus, mollis, magno et peramaeno flore, odoro given to it in 1701 by Caspar Commelin. The genus Lathyrus contains about 150 species. 

Wild sweet peas have been traced back to Sicily, China, Malta, Sri Lanka and elsewhere, but the true origins of the species are lost to history. The first printed reference, though, is attributed to sicilian monk Francisco Cupani who was in charge of a botanical garden n Sicily. Cupani published a written description of the plant in 1699 and sent seed to other European botanists and its cultivation was begun. Sweet peas would eventually become the most widely grown of garden flowers worldwide.

From these “original” plants were developed what were known as the grandiflora but are now generally called the Old-Fashioned Sweet Peas

1999 is the tercentenary of the introduction of the sweet pea to England. The original introduction had rather small flowers, but was very strongly scented. Much early work in genetics was done at Cambridge University, using sweet peas as the subject. Sweet peas come in a very wide range of colours, but not yellow. Early expectations of being able to breed a yellow sweet pea by conventional means were already fading rapidly by 1915.

Sweet pea flowers naturally self pollinate while still in bud. Sweet peas are not edible, being somewhat poisonous if eaten in quantity. Sweet peas are widely grown in Japan, Australia, New Zealand and the USA. By 1913 about 1700 acres of sweet peas were being grown in California to meet the annual demand for some 450 tons of seed, about half of which went to Europe, mostly to England. Market research consistently finds sweet peas to be one of the top three favourite flowers in the UK.

Source:
http://www.baacks.com/thelanguageofflowers/ item.nhtml?profile=thelanguageofflowers&UID=125
http://www.edirectory.co.uk/chilternseeds/pages/ moreinfo.asp?Table=Product&RecordID=BFBBDDE
http://www.farmersmarketonline.com/bk/SweetPeaBook.htm