Development of reproductive structures in the sole Indian species of Hydatellaceae, Trithuria konkanensis, and its morphological differences from Australian taxa

Abstract

The current paper presents new morphological and developmental data on the sole Indian species of Hydatellaceae, T. konkanensis Yadav & Janarthanam, and explores its morphological differences from Australian members of the family. On the basis of morphology and ecology, T. konkanensis appears to be closely related to T. lanterna, a species from tropical northern Australia that resembles T. konkanensis more closely than does any other Australian taxon. However, fruits are dehiscent in T. lanterna and indehiscent in T. konkanensis. Developmental data on T. konkanensis are significant for interpreting the reproductive units in Hydatellaceae. In T. konkanensis, each reproductive unit consists of two bract-like phyllomes, several carpels and a single central stamen that is initiated before the carpels. The earliest-formed carpels are those closest to the stamen; the latest-formed carpels are closest to the phyllomes. Despite their apparently whorled arrangement, the phyllomes are initiated sequentially. The spatial arrangement of the earliest-initiated carpels makes it unlikely that the phyllomes subtend any axillary structures. So far, there is no robust direct evidence in favour of a multiaxial (pseudanthial) morphological interpretation of bisexual reproductive units of Hydatellaceae. No evidence for dichogamy is present in bisexual reproductive units of either Indian or Australian Hydatellaceae, a feature that contrasts with the common presence of protogyny in flowers of other early divergent extant angiosperms.