Passerina quadrifaria (Thymelaeaceae): a new species from the southern Cape and Little Karoo in South Africa

Passerina L. is an endemic southern African genus, with the exception of two species that have outliers in eastern Africa. The genus comprises about 20 species and four subspecies. P . quadrifaria Bredenkamp and Van Wyk is a new species occurring in the Karoo Mountain, Langeberg and Southeastern phytogeographic centres of the Cape Floristic Region. It is most closely related to P . comosa C.H.Wright as the leaves and bracts of both species are abaxially hairy. The most obvious diagnostic feature of the new species is the distinct four-ranked appearance of the leaves, which are decussate, imbricate, sessile and spreading at an angle of ±45°. The species have complementary nonoverlapping ranges, P . comosa occurring from the Kamiesberg of the Northern Cape Province to the Roggeveld, Witteberg and Klein Swartberg mountain ranges of the Western Cape Province, whereas P . quadrifaria is restricted to mountain ranges of the southern Cape and western parts of the Eastern Cape Province. There are two morphologi-cal forms of P . quadrifaria , the first form corresponding to the general species description and a second form with slightly longer internodes, smaller leaves and the apices of the bracts more rounded. As the leaves of these two forms are anatomically identical, they are not given formal taxonomic status. atis, internodis perbrevibus. Folia decussata, imbricata, ad angulum 45° divergentia, sessiles; basis rhombea, dilatata, accurate interordinata basibus foliorum nodorum proximo-rum; cymbiformes, circumscriptione lineari-lanceolata; lamina inverse ericoidea, pagina adaxialis concava, setosa, pagina abaxialis convexa, foliis juvenibus tomentosa; apex rotundatus; margines ciliati. Bracteae cymbiformes, circumscriptione ovatae vel late ovatae; lamina adaxialiter conca-va, comosa, abaxialiter convexa, sparsim pubescens ad tomentosa, ± tricostata utrinque costae, coriacea rugosaque, in marginem membranaceum expansa; basis cuneata; costa excurrens apicem rotundatum vel subacutum faciens; margines ciliati. Flores papyracei, tempore pollina-tionis luteo-rosei, postea rubescentes vel


Introduction
This paper forms part of a monographic study of Passerina L. (Bredenkamp and Van Wyk 1999, 2001a in which four new species and four new subspecies have been added to the existing 16 species (Thoday 1924, Goldblatt andManning 2000). With the exception of P. montivagus Bredenkamp and Van Wyk, the new taxa are all endemic to the Cape Floristic Region. Under the heading 'Incertae', Thoday (1924) discussed certain specimens mostly from mountain summits, pointing out their possible relationship to P. comosa C.H.Wright as well as to other species and concluded that further field work might shed more light on their identity. In the present study these specimens proved to be a new species, morphologically distinct from P. comosa and geographically isolated from it. Weimarck (1941) considered P. comosa as a 'north-western endemic' within the Cape flora and this is confirmed by the present study. The new species is restricted to the mountains of the Little Karoo and southern Cape. The presence of an abaxial indumentum of the leaves and bracts in the new species has led to its confusion with P. comosa, but it can be distinguished from the latter by evidence from leaf anatomy (Bredenkamp and Van Wyk 1999, 2001a as well as floral morphology (Bredenkamp and Van Wyk 2001b).

Material and Methods
Passerina material from the following herbaria was studied: BOL, G, GRA, M, NBG, PRE, TCD. Extensive field work was conducted and live material of the new species was collected and preserved in formalin-alcohol-acetic acid (FAA) ( Table 1). Leaves and flowers were fixed and stored in a 0.1 M phosphate-buffered solution at pH 7.4, containing 2.5% formaldehyde, 0.1% glutaraldehyde and 0.5% caffeine [modified Karnovsky fixative; Karnovsky (1965)]. Leaves preserved in the modified Karnovsky fixative, as well as from rehydrated herbarium material, were used for the anatomical study.

Diagnostic characters and relationships
Both Passerina quadrifaria and P. comosa have abaxially hairy bracts, hence they are easily confused. However, Leaf anatomy, epidermal studies Stokoe 9302 Leaf anatomy, epidermal studies All specimens are housed at PRE these two species are geographically isolated, with P. comosa considered as a 'north-western endemic' of the Cape flora (Weimarck 1941), while the distribution of P. quadrifaria is along the mountain ranges of the southern Cape and western parts of the Eastern Cape Province.
Morphologically P. comosa is less robust, internodes are longer, leaves adhere closely to the stem and are generally more hairy and the bracts often have extended wings that are abaxially setose. All the specimens characterised by abaxially hairy bracts and occurring in mountainous areas of the Little Karoo and southern Cape, showed considerable variation. In the present study all these specimens were grouped under P. quadrifaria, but two forms could be recognised within this species. The first form corresponds to the present species description. Schlechter 5846, Keet 1067 and Esterhuysen 10734, 27971 and 27383 represent the second form, characterised by slightly longer internodes, smaller leaves and the apices of the bracts are more rounded (resembling P. montana). None of these characters are constant and many specimens represent intermediates between the two forms. Leaf anatomy does also not provide additional characters to justify the recognition of these two forms at species level Van Wyk 2000, 2001a).
Passerina quadrifaria may also be confused with stunted forms of P. obtusifolia Thoday, a species occurring in dryer areas of the Eastern Cape. The leaves of these plants also have a four-ranked appearance, but the shape and especially the obtuse apex of the leaves and the bracts, clearly identify P. obtusifolia.

Etymology
The specific epithet is derived from the Latin quadrifarius = in four ranks. The name describes the decussate arrangement of the leaves, which almost gives the impression of a spinal column found in lower vertebrates.

Distribution and ecology
Passerina quadrifaria is distributed in a belt between 33° to 34°S latitude and 20° to 24°E longitude, on the mountain ranges of the southern and eastern parts of the Western Cape and the southern and western parts of the Eastern Cape, including the Langeberg, Swartberg, Kouga, Outeniqua, Tsitsikamma and Groot Winterhoek Mountains. The range includes the Karoo Mountain, Langeberg and Southeastern phytogeographic centres of the Cape Floristic Region (Goldblatt and Manning 2000). Plants grow at high altitudes of 1 500-1 670m, in rocky places, often on southeast-facing rocky slopes and the summits of peaks. Summer drought has a major influence on the vegetation of the mountain fynbos (Rebelo 1998), possibly contributing to the xeromorphic appearance of P. quadrifaria, such as its shortened branchlets and internodes, as well as sturdy, decussate and coriaceous leaves. On the northern side of the Swartberg Mountains, fynbos is replaced by karroid vegetation and it is in these areas that P. quadrifaria can easily be confused with P. obtusifolia, a species largely confined to more arid karoo conditions (Figure 3).