Abstract
Acalypha (Euphorbiaceae) consists of approximately 450 species. Acalypha indica L. is a common annual herb (1-3 ft high). The plant develops a peculiar terminal monocarpellary female flower at the tip of inflorescence axis, it is known as allomorphic flower. Actually, the species produces two kinds of female flower, viz. the allomorphic flower and lateral, tricarpellet regular euphorbiaceous (female) flower. Interestingly, two kinds of female flowers exhibit two opposite mode and direction of evolutionary trends. The lateral flower shows regressive evolutionary trend while the terminal flower shows the trend of progressive evolution. The allomorphic flower, from either progressive or regressive view, stands in a different state of evolution from other flowers; this is a case of heterobathmy. And, both kinds of flowers are under neutral selection pressure, and the development of unicarpellary flower in this Euphorbiacean member is a kind of neutral evolution.
