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BORANUP BOSSIAEA (BOSSIAEA DISTICHA): DISTRIBUTION AND BIOLOGY By GREG KEIGHERY Department of Conservation and Land Management. PO. Box 51. Wanneroo. 6065. ABSTRACT The distribution of the restricted plant, the Boranup Bossiaea (Bossiaea distic/ia) is detailed. The species contains three distinct forms.oneaprostratecoastal ecotype,theothersdifferingin flower colour. While largely centred on the Boranup Forest, the species extends along the Leeuwin-Naturaliste Ridge to the north and south. The species is well conserved in Leeuwin-Naturaliste National Park. INTRODUCTION shown in Figure 1. Unlike previous assumptions the species is not Bossiaea disticfia is a striking feature of confined to the Boranup Forest, but the Karri forest in the Boranup area extends from Ellen Brook to Cape in spring, where it often forms a Leeuwin. along the southern half of dominant component of the lower the Leeuwin-Naturaliste Ridge, a shrub layer. The species has a very range of 55 kilometres. Interestingly restricted range (Keighery, 1981) com¬ Bossiaea distic/ia does not cross the pared to many other members of the Blackwood estuary (However, three Fabaceae of Western Australia. It has feral plants are established on the been thought of as restricted to the verge of Dalton Road, south of Scott Boranup State Forest, and has been River Road, in this area) despite ap¬ listed in many rare plants reports as parently suitablehabitat(Karri forest) actually or potentially rare(Marchant being present on the adjacent shore. and Keighery, 1979 and Briggs and The poorly drained clayey soils and Leigh, 1981). However, little detailed occasional inundation of this area are survey has been undertaken on this not able to be colonised by Bossiaea species. In 1990 as part of a wider distic/iawhichdoesnotgrowinwinter survey of the rare flora of the Scott wet or poorly drained sites.This Plains (Keighery and Robinson, 1992) coNfines the species to the well I was able to undertake a survey of drained loams and granites of the the distribution of Bossiaea distic/ia. Leeuwin-Naturaliste Ridge, west of the Black-wood River, in the southern portion of its range. The DISTRIBUTION AND VARIATION northern limit of the species range OF BOSS/AEA DISTICHA corresponds to the 1,000 mm isohyet, The distribution of Bossiaea disticha is and the eastern limit, in this area, by 97 Figure 1. Distribution of Bossiaea distic/ia Area A; brown flower colour form. Area B: yellow flower colour form. 98 the decreasing rainfall and the lack status is given to these variants; rather of suitable soils (granites and Karri they should be conserved as distinct loams). All of these factors restrict the local variants of this species. occurrence of Bossiaca disticha to the The few other documented cases of southern half of the Leeuwin- geographically based variation in Naturalista Ridge. flower colour of native peas also have Only Acacia subraccmosa (truly not been given formal taxonomic confined to the Boranup Karri Forest) status. Keighery (1985) demostrated and Kennedia macrophylla (confined that the Middle Island form of to Cape Leeuwin) have more re¬ Kennedia nigricans has a orange rather stricted ranges in the area. The Acacia than the yellow eye on the mainland is abundant in the Boranup Forest, and breeds true from seed. The Cape and well conserved. However, the Range form of Su^aisonia (Cliant/ius) Kennedia occurs as scattered disjunct formosus has a red rather than the populations and is legally protected black boss found throughout the rest as rare flora. of the species' range. This form also Bossiaca disticha grows in Karri breeds true from seed. (Eucalyptus diversicolor) forest, Marri Another variant is found in coastal (Eucalyptuscalophylla) forest, low forest granite heath on Cape Leeuwin and or woodland and granite heath. As Cape Freycinet. This is a prostrate or noted previously the limits on the low spreading shrub with short occurrence of this species seems internodes, giving the plant a very mainly determined by rainfall and leafy appearance. Material form Cape soil type. Freycinet retains this habit when Within this area two distinct flower grown from seed, suggesting the trait colour forms occur, as illustrated in is genetically fixed. Figure 2. The northern colour form Despite this species restricted range it has brownish flowers and is found does contain a number of distinctive, only in the Ellen Brook area. Fortun¬ interesting variants, all of which ately most populations occur within fortunately occur within conser¬ Leeuwin-Naturaliste National Park. vation reserves. This species despite Southern populations have flowers its limited range, seems to be with distinct yellow markings, and adequately represented in conser¬ are relatively uniform throughout vation reserves. the remainder of the species' range, as shown by the dashed lines on the BIOLOGICAL NOTES accompanying map. Both of these colour forms are pollinated by the Bossiaea disticha is a single stemmed same suite of solitary bees (Tricholettes shrub, killed by fire, that produces sp), and probably repre-sent minor hard seeds which germinate pro- genetic differences. Though the lifically the following winter. These colour differences are striking on produce dense even aged stands of living material dried flowers fade to a plants. Flowering commences the uniform brown after several years second spring after a summer fire, but and onecannot easily ascribe the type can commence the spring after a collection with its vague locality to spring fire the previous year. Plants either form. Hence no taxonomic reach maximum seed production 5 99 Figure 2. Flower Colour Forms of Bossiaea disticha. (1) Northern Brown Flowered Form. (2) Southern Yellow Form. 100 to 7 years after a fire event, and Keighery.G.J. 1985. Kennedia nigricans continue to flower and seed for at - Insular Form. Australian Plants 13: least another 5 to 7 years. There is no 59. longer term data than this at present. KEIGHERY. G.J. and ROBINSON. C.j. 1992. Declared Rare Flora and Other Plants in need of Special Protection REFERENCES of the Scott plains. Report to the BRIGGS. J. and LEIGH. J. 1988. Rare or Australian National Parks and Wild¬ Threatened Australian Plants. Aus¬ life Service, Endangered Species tralian National Parks and Wildlife Program by Department of Conser¬ Service Special Publication No. 14. vation and Land Management, Perth. Canberra. MARCHANT, N.G. and KEIGHERY, KEIGHERY, G.J. 1981. Distribution G.J. 1979. Poorly Collected and Pre¬ Maps of the Fabaceae of Western sumably Rare Vascular Plants of Australia. Kings Park Research Notes Western Australia. Kings Park Re¬ 6:1-120. search Notes 5:1-102. 101