The significance of a new umbellate ornamentation in Isoetes (Isoetaceae: Lycopodiopsida) megaspores

Abstract A new umbellate ornamentation pattern is described in Isoetes megaspores based on scanning electron microscopy and thorough comparisons with sculptural patterns documented in lycophytes and ferns. The umbellate ornamentation is quite distinct from other vertically projected megaspore sculptural patterns (baculate, clavate, gemmulate, pustulate, tuberculate, saccate and verrucate). In addition, megaspore ornamentations described previously for I. dixitei as tuberculate or pustulate have now been corrected as umbellate. This species also possesses a rudimentary velum and internal pigmentation in sporangial wall which has not been reported in other Indian species of the genus. Further, this taxa has a range restricted to the Western Ghats and is confined to a higher elevational range than Indian species characterised by vertically projected megaspore surface ornamentation patterns.