EARLY DEVELOPMENT AND APICAL GROWTH IN PHYLLOSPORA-COMOSA (LABILLARDIERE) AGARDH,C. (SEIROCOCCACEAE, PHAEOPHYTA)

Morphology and development of Phyllospora comosa juveniles, and adult apical growth was investigated using light and electron microscopy and histochemistry. Juvenile plants followed a pattern of adhesion and de velopment consistent with other fucoids, and at ten weeks a three-side d apical cell was produced at the plant apex. Serial sectioning of adu lt apices showed four-sided apical cells. Receptacles and lateral axes are derived from apical initials which pass from the apical groove on to the axis margin. Vegetative laterals originate from outgrowths in the apical grovve. Presence of four-sided apical cells is unusual amon g southern hemisphere fucoids and is more common in northern hemispher e genera of the Fucaceae. Change from a three-sided apical cell in juv eniles to four-sided apical cells in adult plants is also similar to m embers of the Fucaceae, and may represent a derived feature. Similarit y between the Seirococcaceae and the Fucaceae could suggest either a c ommon ancestry or alternatively an example of convergent evolution.