Psychophily in Stachytarpheta jamaicensis (L.) Vahl. (Verbenaceae)

Stachytarpheta jamaicensis is a seasonal shrub which produces flowers for a lengthy period during rainy and winter seasons. The floral characteristics such as bluish-violet flowers, no perceptible smell, narrow tubular corolla and concealed nectar accumulated at the corolla base conform to 'psychophilous pollination syndrome'. The aggregated arrangement of flowers on the inflorescence is economical and energetically rewarding for the butterflies. The lower lip of the corolla is elaborate and provides comfortable landing place for the butterflies. The nectar is sucrose-rich with 28% sugar concentration and also carbohydrate-rich with little protein content. It is also an important source of five of the ten essential amino acids required by butterflies; they include isoleucine, valine, lysine, methionine and threonine. Further, it also contains the non-essential amino acids such as alanine, butyric acid, cystine, glutamic acid, glysine, hydroxyproline, proline, serine, aspartic acid and cysteine. With these floral morphological and functional characteristics, the plant is exclusively pollinated by butterflies. Among butterflies, nymphalids and pierids are relatively more diverse in species and consistent foragers than papilionids and hesperiids. Therefore, the interaction between S. jamaicensis and the butterflies is mutualistic; the former for pollination and the latter for nourishment. This floral source is available for a long period and hence is an important nectar source for the maintenance of local butterflies. Additionally, bees also visit the flowers for forage and their visits could contribute to gene flow at population level to some extent. S. jamaicensis produces fruits with minute seeds within a short span of time. Seed dispersal occurs through soil and water movement. They germinate immediately if the soil is sufficiently wet; if not, they remain dormant until the soil is charged with water during monsoon season. The plant with abundant seed production enjoys a 'minor weed' status only.