Biogeography and composition of the flora of the Cape Range peninsula, Western Australia

WA Museum Records and Supplements | Updated 9 years ago

Abstract - The Cape Range peninsula is here considered as the area north of a line joining Ningaloo Homestead and the base of Exmouth Gulf. The Cape is dominated by a series of limestone hills of moderate to low relief, surrounded by sandplain or coastal plains. The Cape Range itself is vegetated with Eucalyptus over Triodia , with Acacia- Cassia shrubs as understory or locally dominant. The lower ranges are vegetated with Acacia shrublands over Triodia. The coastal plain is vegetated with grasslands, coastal strand vegetation, low shrublands (including Samphires and Saltbush) and Mangrove low forest and the sandplain by heath over Triodia.

Six hundred and thirty taxa of vascular plants have been rccorded from thc pcninsula, a rich flora The flora is dominated by widespread dcsertic elements, Ixlth of a tempenue and tropical nature, reflecting the geographic position of the peninsula and the general composition of the flora of the Carmuvon Botanical District. Analysis of thc composition of thc flora indicates it is most similar to the flora of Barrow lsland, and othcr coastal sites at Lakc Macl_cod and the Bun-up Peninsula. A distinct feature of the flora is a group of taxa that occur from Shark Bay to North West Cape. Another related group links the flora of the Geraldton area to that of Shark Bay.

The peninsula has 12 endemic taxa and six taxa largely confined to the peninsula. All taxa are listed and distribution patterns compared in this paper.

The flora also encompasses a significant number (50) of taxa of southern temperate affinities here at the end of their ranges. Most of these taxa extend from the Geraldton area to North West Cape. These taxa occur on the sandplain (Banksia ashbyi, Emblingia calceoliflora ), or the western coastal dunes (Santalum spicaturn, Scaevola crassifolia ) rather than on the massive limestone hills. In addition the peninsula has a number of unusual disjunctions associated with Yardie Creek. These are several taxa of freshwater emergent aquatic species and, remarkably, the Millstream Palm.

Few weeds have been recorded from the peninsula, 30 taxa are listed, most of which occur around the townsite of Exmouth. Significant weed invasion has also occurred in the Yardie Creek gorge with infestations of Emex australis and Asphodelus Jistulosus and on the western coastal plain, where Buffel grassland has replaced the native Triodia grassland.

A brief site based survey of the limestone surfaces of the study area has revealed significant floristie differences between the Ranges. Distinctive groups are associated with the Coral Bay limestone outcrops; the Gnargoo and Giralia Ranges; central Cape Range; Rough Range and the western coastal plain of the peninsula; and sand over the limestone on Cape Range. Future studies on the floristics of the sandplain and coastal plain areas would be rewarding. A study to place the floristies of the peninsula within the wider context of the Carnarvon Botanical District is also needed.