Evolution of prostrate and erect habits in Cotula section Leptinella and other New Zealand plant groups

Abstract

Plants of Cotula section Leptinella have evolved a prostrate habit from suberect ancestors. Seedlings establish the prostrate habit after several crowded leaves have been produced; an inflorescence is initiated and horizontal branches with long internodes grow out from the flowering node and several nodes immediately behind it. Cotula featherstonii has secondarily evolved an erect woody habit; seedlings produce long internodes on the pnmary axis without flowering and stems remain erect. Many other genera in New Zealand have evolved a reduced stature, in some instances including prostrate habits. The reverse direction of evolution towards increased stature and woodiness has probably occurred less frequently. In this respect, New Zealand may be exceptional among isolated islands because of its continental origin and the relatively recent appearance of xeric and montane conditions favouring reduced stature.

Keywords:

• Cotula
• Compositae
• prostrate habit
• erect habit
• woodiness
• morphology
• New Zealand
• islands