Regional endemism in New Zealand grasses

Abstract

Regional endemism is evident in 60 grass taxa among the 182 species and infraspecific taxa that comprise the New Zealand endemic grass flora. The pattern of regional endemism matches that described earlier for dicotyledons with high frequencies in Nelson‐Marlborough of northern South Island, and in southern South Island in Otago, Southland, and Fiordland. Low frequencies in southern North Island and central South Island are also consistent with patterns earlier described. In northern North Island grass endemism is low, consistent with the long history of forests in that region. Habitat preference is evident for most regional endemics with rupestral and edaphic constraints dominating. Taxonomic rank is the first imperative in establishing status as a regional endemic. Disjunctions fragment species into genetically isolated populations with their own evolutionary potentialities. These populations, unadorned by taxonomic rank, are treated as simple species disjunctions unlike those supported by an infraspecific taxonomic foundation that qualify for regional endemism. This distinction seems biologically inconsistent. Regional grass endemics conform in chromosome number, reproductive biology, and habitat selection to other congeneric species except for rare departures. A comparison of the frequencies in regional distributions of endemic Gramineae and endemic herbaceous Compositae showed a high level of agreement, unlike that with endemic Cyperaceae. Among the tribes of New Zealand Gramineae, Agrostideae have a lower ratio of regional endemics:total endemics than in tribes Poeae and Danthonieae, primarily because of the lack of coherent morphological‐geographic patterns in species of wide amplitude.

Keywords:

• regional endemics
• disjunct distribution
• grasses
• phytogeography
• biogeography
• New Zealand