Taxonomy of the Passerina filiformis complex ( Thymelaeaceae )

Revision of the genus Passerina L. indicated a new delimitation of taxonomic entities within the Passerina filiformis L. complex. Evidence from leaf anatomy greatly assisted in the recognition of taxa. P. filiformis is here divided into two sub­ species. namely P. filiformis subsp. filiformis and P. filiformis subsp. glutinosa (Thoday) Bredenkamp & A.E.van Wyk. and a new species. P. montivagus Bredenkamp & A.E.van Wyk, w hich is also described. The new taxa are geographically sep­ arated: subsp. filiformis ranges from Piquetberg in the north through the Cape Peninsula in the south, where it is quite com­ mon. to Attaquaskloof in the southwestern Cape: subsp. glutinosa occurs along the coast between Vredendal and St Helena Bay; and P. montivagus has a wide distribution from Mossel Bay and Oudtshoom in the south through Eastern Cape and along the Great Escarpment northwards to Zimbabwe, with outliers in Tanzania.


INTRODUCTION
Passerina L., a genus of woody shrublets or shrubs, comprises about 20 species and four subspecies, all con fined to southern and eastern Africa (Thoday 1924;Goldblatt & Manning 2000).With the exception of a few species grow ing along the Great Escarpment, most mem bers are endemic to the Cape Floristic Region with its Mediterranean or semi-Mediterranean climate.In the most recent taxonomic revision of the genus, Thoday (1924) considered P. filiformis L. a variable species with a wide range, noting that plants from KwaZulu-Natal are more robust and luxuriant in grow th.The purpose of the present paper is to present a taxonomic re-assessment of the P. filiformis complex based on evidence from epider mal structure (Bredenkamp & Van Wyk 1999. 2()(X)).leaf anatomy (Bredenkamp & Van Wyk 2001a) and floral morphology (Bredenkamp & Van Wyk 2(K)lb).We pro pose the subdivision of P. filiformis L. into two sub species and describe a new species; all the new taxa are geographically separated (allopatric).

MATERIAL AND METHODS
All collections of Passerina in the follow ing herbaria (acronyms according to Holmgren et al. 1990) were studied for taxonomy and external morphology; BM.BOL, BREM, C. GRA.K. LINN.M. MO.NBG.PR.PRE.PRU. S. SBT.TCD.UPS.
For leaf anatomy, both fresh and herbarium material were studied.Names of taxa and voucher specimens used in anatomical studies are listed in Table 1.
Light microscopy (LM) was used for general leal anatomical as well as epidermal studies.Methods for preparation of transverse sections and lor the study of cuti cles are described by Bredenkamp & Van Wyk (2000).Scanning electron microscopy (SEM) was used to study epidermal surface features (including epicuticular waxes) and to elucidate the structure of the cuticle (Bredenkamp & Van Wyk 2000).Transmission electron microscopy (TEM ) was used to establish the structure of mucilaginous epidermal cell walls (Bredenkamp & Van Wyk 1999).

L ea f anatomy
Leaf structural type B: bundle sheath completely enveloping main vascular bundle, extraxylary sclerenchyma fibres enclosed in bundle sheath (Bredenkamp & Van Wyk 2001a).
Two of the four Passerina specimens in the Linnean Herbarium are named P. filiformis in the handwriting of Linnaeus; these specimens are numbered 504.1 and 504.2 in Savage (1945).Number 504.2 is undoubtedly P. paleacea Wikstr.Thoday (1924) maintains that number 504.1 is a Clifford specimen and probably the one Linnaeus saw when he wrote the first edition of Species plantarum (1753).Savage (1945) added the inscription (? ex herh.Cliff.), indicating doubt as to the origin of this specimen.The first author has seen this specimen and agrees w ith Thoday (1924) that it matches the concept of P. filiformis perfectly, as it is known in the Cape Peninsula.The phrase 'Passerina foliis linearibus' in the Species plantarum (1753).has clearly been copied by Linnaeus from Hortus Cliffbrtianus (1738) and from Van Royen (1740).The leaves in the illustration in Hortus Cliffortianus are ± lanceolate and the bracts are very simi lar to those of P. filiformis subsp.glutinosa (Thoday) Bredenkamp & A.E.van Wyk stat.nov., w hich has acerose or filiform leaves.The specimen labelled Passerina fili form is L. in Clifford's Herbarium is sterile, lacks charac teristic bracts or flowers and could possibly be P. vulgaris Thoday (= P. filiformis L. subsp.vulgaris Meisn.).P. vul garis is the dominant Passerina species in the southern and southwestern Cape and is constantly confused w ith P. filiformis.Specimen 504.1 in the Linnean Herbarium, w hich is named P. filifomis by Linnaeus, is here designat ed as the lectotype.Thymelaea aethiopica, in Plukenet (1700: 180). is cited in synonymy under P. filiformis by Linnaeus (1753).The illustrated synonym of Breyne (1678) most probably belongs to the genus Phylica L. (Rhamnaceae) and that of Burman ( 1739) is clearly a species of Struthiola L. (Thymelaeaceae).
Diagnostic characters and relationships: subsp.fili formis is morphologically distinguished by the almost terete, adaxially grooved, acerose or linear leaves, the cymbiform.w idely obovate floral bracts, which abruptlv narrow to a filiform point (Figure 1A-C).and by the long (± 1.7 mm) hypanthium neck.As both subsp.fili formis and P. vulgaris occur in the Cape Peninsula, they are often confused.Diagnostic characters of P. vulgaris include linear to narrowly lanceolate leaves, the diamond-shaped bracts and leaves with a hypodermal scle renchymatous sheath (Bredenkamp & Van Wyk 2001a).Some specimens of subsp.filiformis with incurved, tapering leaves and the necks of the hypanthium exsert ed from the clasping, veined bracts, could be mistaken tor P. falcifolia.The apical beard on the young leaves and outer sepals and the glabrous inner sides of the bracts are reliable diagnostic characters, distinguishing the subsp.filiform is from P. falcifolia.Leaves glutinous, closely adhering to stem or spread ing at angle of ± 30°; lamina narrow, acerose or linear, transversely elliptic in c/s, length x 7: width ± 7.0 x 0.4 mm, tapering towards rounded apex, widening towards base, dark green, drying brown.Inflorescences glutinous, somewhat longer than in typical subspecies.Bracts ovateacuminate, gradually narrowing to point, length x 72 width ± 4.6 x 1.5 mm, base cuneate, main vein strongly developed; lamina coriaceous; wings membranous, with distinct venation; margins often ciliate.Flowers gluti nous.Floral envelope ± 6.5 mm long, sparsely tomentose at ovary, neck 1.5 mm long, sparsely tomentose, outer and inner sepal lobes concave-obovate.Figure 1D-F.
Thoday 215 in NBG was chosen as lectotype because of the longer inflorescences and the conspicuously gluti nous, narrow leaves.Duplicates of the syntype of var.glutinosa, Schlechter 5 /2 5 , from BM, C, K. MO, PRE and S were seen.Although these specimens agree close ly with the concept of var.glutinosa (Thoday 1924), the glutinous character is not evident in the dried specimens.
L ea f anatomy L eaf outline in t/s transversely elliptic.Adaxial epi dermis with CM ± 2 pm thick; periclinal x anticlinal cell diam. in t/s 15 x 10 pm.Abaxial epidermis, in surface view, glutinous (Figure 2C), cells slightly oblong, 50 x 30 pm: CM 15 pm thick in t/s.periclinal x anticlinal cell diam.40 x 55 pm.Palisade parenchyma in 2 layers of elongated cells.Main vascular bundle ± 400 pm thick.± 820 pm wide, sunken into palisade parenchyma abaxially (type B4) or bordering on abaxial epidermis (type B6) (Figure 2B).Bundle sheath consisting of ± 27 cells, adaxially radiating outwards, abaxially tanniniferous, specializing into collenchyma in contact with abaxial epidermis.Secondary vascular bundles 2 or 3 on each side of main bundle.
Distribution and ecology: subsp.glutinosa occurs in the Strand veld (Acocks 1988), from Doring Bay in the north to St Helena Bay in the south.The vegetation sur rounding Doring Bay is described as Strandveld Succulent Karoo by Hoffman (1998).The area is charac terized by deep, calcareous, coastal Quaternary sands and generally low rainfall.St Helena Bay is situated in the Sand Plain Fynbos (Rebelo 1998).This part of the range has a Mediterranean-type climate with summer drought and deep acid sands.Sand Plain Fynbos is a highly endangered vegetation type because of urbaniza tion and the impact of alien invasive plant species (Rebelo 1998).
Diagnostic characters and relationships: Passerina montivagus is easily distinguished from P. filiform is by its more robust and luxuriant habit.Furthermore, for some distance below the inflorescences, the foliage leaves are expanded at the base and the bracts are ovate to obovate, narrowing gradually into a sturdy, leaf-like point, with margins along their distal half conspicuously fringed by strong white trichomes.P. montivagus could also be confused with P .falcifolia,but it is distinguished from the latter by the apical beard on the young leaves and outer sepals and by the adaxial surfaces of the bracts, which are basally setose with glabrous wings.
Etymology: the specific epithet is a compound of the Latin montanus (= pertaining to mountains) and vagus (= in several directions), referring to the distribution of this species.Von Breitenbach et al. (2001) uses the names brown gonna (English), bruingonna (Afrikaans) and unwele oluncane (Zulu) for P. filiform is in the wide sense, but these names are most appropriate for P. montivagus because of its wide distribution.
Distribution and ecology: Passerina montivagus has a wide distribution, from Mossel Bay and Oudtshoom in W estern Cape northw ards mainly along the Great Escarpment to KwaZulu-Natal, Swaziland, M puma langa, Northern Province, Mozambique and Zimbabwe.
Polhill & Paolo 2372, from Tanzania, represents an extreme form of this taxon, as the bracts are smaller and almost diamond-shaped.The most southwesterly distri bution of this species is in the southern Cape, a region transitional between w inter and sum m er rainfall.However, over most of its range, the species receives summer rainfall.Because of its wide distribution, espe cially along the Great Escarpment, P. montivagus is adapted to a variety of habitats, with relatively high rain fall.It is often found along forest margins in the ecotonal zone between Afromontane forest and grassland.It has been recorded from rocky mountain peaks and slopes, river valleys, gorges and among riverside rocks.In coastal regions, it grows on hills and often borders small tributaries of streams flowing to the sea. Figure 5. Story (1952) reported that P. montivagus (= P. fili form is) dominated the western half of a small plateau north o f the M ount M cDonald beacon in the Keiskammahoek District.The plants were not browsed by stock although the plateau was heavily grazed.He regarded the species as 'useless' and advised that it should be eradicated by hand, as it was not dense enough to bum without additional fuel.This Fynbos species, dis tributed along the Great Escarpment has not been report ed as undesirable or invasive and is currently not regard ed as a threat, although it might be a dominant species in restricted areas.
Etymology and uses: according to Van Wyk & Gericke (2(MX)) the name bakkerbos commemorates an era in the Cape when the official licensed bakers used the branches
distribution o f P .filiform is subsp.glutinosa.

s* FIGURE 2.__LM photographs and SEM micrographs showing leaf anatomy and epidermal structure of selected species in Passerina: A, P fili- form is subsp. filiform is, Bredenkamp 1039, leaf in
(Smith 1966)is plant to heat their ovens.The plants used at that time were clearly the subsp.filiformis.When ignited, plants of subsp.filiform is disappear in a blaze of hot flame owing to a waxy secretion on the leaves(Smith 1966).The plants were formerly used for heating up stoves.Today it is quite scarce in the vicinity of Cape Town, because of the commercial use of this once abun dant resource.At maturity, these plants are quite orna t/s, illustrating leaf structural type B4.B, C, P .filiform is subsp.glutinosa,Schlechter 5125: B, leaf in t/s, from rehydrated herbarium material, illustrating leaf structural type B6 ; C, glutinous substance sticking pollen grain to leaf surface.D, P. montivagus, Bredenkamp 1016, leaf in t/s illustrating leaf structural type C. E-H , abaxial epidermis in P. montivagu s: E, in surface view, with cells arranged in rows, Bredenkamp 1012; F, epidermal cells oblong, pentagonal to heptagonal, Bredenkamp 1016; G, upright epicuticular wax platelets, Bredenkamp 1016.H, mucilagination of inner tangential cell walls, resulting in mucilagefilled cavities, Killick 238.ad, adaxial epidermis; ab, abaxial epidermis; bs, bundle sheath; m, mucilage; mb, median vascular bundle; pi, epicuticular wax plates; pp, palisade parenchyma; sp, spongy parenchyma.Scale bars: A, B, D-F, H, 100 pm; C, G, 10 pm. and mental and have been cultivated in Britain and Europe since the time of Linnaeus.Plants of the subsp.filiform is are soboliferous and vigorous resprouters.They are well adapted to the Cape climate and would be suitable for reclamation plantings in areas where alien invasive vege tation has been cleared.The tough bark was used by indigenous peoples instead of twine (Marloth 1925).According to Laidler (1928) a decoction o f this plant is used by the rural people of the Cape for shooting pains.P.