Introduction

A notable feature of tropical alpine floras in many parts of the world is the presence of rosette plants with monocarpic growth habits. These long-lived perennials flower only once in their lives, producing a giant inflorescence with large numbers of flowers before the parent plant dies. In the South American páramos of Venezuela, species of Espeletia (Asteraceae) provide classic examples of this life-form (Cuatrecasas 1986; Berry & Calvo, Chapter 13)). Giant species of Afroalpine Lobelia (Campanulaceae) reach to 5–6 m in height when flowering before dying, and form one of the most spectacular elements of the flora of the tropical African highlands (Mabberley 1974; Young, Chapter 14). On Tenerife in the Canary Islands, two alpine species of Echium (Boraginaceae) have also evolved rosette growth forms and a monocarpic habit (Carlquist 1974). In each of these groups, the monocarpic rosette plants have evolved from polycarpic ancestors with a shrubby growth form.

Argyroxiphium sandwicense (Asteraceae) provides another well-known example of the evolution of a monocarpic rosette plant in a tropical alpine environment. The genus Argyroxiphium, with five species, is one of three genera of Hawaiian tarweeds that have evolved from a monophyletic North American origin (Carr 1985; Witter & Carr 1988; Baldwin et al. 1991). This group displays a remarkable diversity of growth forms and adaptive morphologies. Monocarpic rosette plants have evolved not only in species of Argyroxiphium in bog and in alpine habitats, but also in Wilkesia gymnoxiphium, a stalked rosette plant in scrub and open forest habitats.