Botanical Journal of ike Linnean Society (1991), 107: 1-34. With 54 figures Leaf anatomy of Bruniaceae: ecological, systematic and phylogenetic aspects SHERWIN CARLQUIST, F.L.S. • Rancho Santa Ana Botanic Garden and Department of Biology, Pomona College, Claremont, California 91711, U.S.A. Received August 1989, accepted for publication October 1989 CARLQUIST, S., 1991. Leaf anatomy of Bruniaceae: ecological systematic and phylogenetic aspects. Quantitative and qualitative data are given for 60 species of the 12 genera of Bruniaceae; most data are based on liquid-preserved material. Leaves of Bruniaceae are basically linear (broader forms are probably derived) with an apicula that contains phellogen activity. Most bruniaceous leaves have some degree of isolateral construction, with transition to normal bifacial construction in a few species, but more commonly transition to 'inverse' bifacial structure (stomata on adaxial face, palisade on abaxial face). The latter type is correlated with the tendency for leaves to be appressed to stems. Tannins and very likely other dark-staining materials are very characteristic of mesophyll cells. Six genera have a large strand of fibres on the midvein and rhomboidal crystals in bundle sheath cells. The other six genera have few or no fibres on veins and have druses in mesophyll cells (but not in bundle sheath cells;. These distinctions may relate to intrafamilial taxonomy, but they also support the primitive position usually accorded to Audouinia, Thamnea and Tittmannia. A key to genera based on leaf antomy is offered. Details of epidermal cell shape, cuticular relief and trichome form and structure based on scanning electron microscopy are given. Leaf anatomy, combined with other features, favours a relationship between Bruniaceae and Grubbiaceae in particular and in broader contexts allies Bruniaceae to rosalean and possibly hamamelidalean families. ADDITIONAL KEY WORDS: —Ecological anatomy - Grubbiaceae - Hamamelidales - Pittosporales - Resales. CONTENTS Introduction 2 Material and methods 3 Anatomical descriptions 3 Leaf tip 3 Leaf shape and dorsiventrality 7 Cuticle 11 Waxes 16 Epidermal cell shape 18 Subsidiary cells 18 Guard cells 18 Trichomes 20 Contents of mesophyll and epidermal cells 24 Crystals 25 Veins 25 Ecological conclusions 27 Systematic conclusions 29 Phylogenetic conclusions 32 Acknowledgements 33 References 33 1 0024-4074/91/090001-1-34 S03.00/0 •© 1991 The Linnean Society of London 1 S. CARLQUIST [NTRODUCTION Bruniaceae comprises 12 genera and about 75 species (Bond & Goldblatt, 1984). These small to large shrubs are confined to south-westernmost Africa; most species are characteristic of the montane sandstone areas, but a few can be found on lowland areas and even on laterites. Only one species, Raspalia trigyna, exceeds the borders of Cape Province (Pillans, 1947). The leaves of Bruniaceae are predominantly small and either acicular or scale­ like, although broader leaves occur in species of Lonchostoma as well as in Berzelia cordifolia and Pseudobaeckea cordata. The limited surface area of leaves in most species of Bruniaceae seems related to particular features of the Mediterranean-type climate of Cape Province. The xeromorphy reflected in these leaves is indicative not so much of low annual rainfall but of high summer heat, and low summer humidity. Montane Cape Province is notably windy and sandstone soils are very porous. Nevertheless, during field work in South Africa, one repeatedly sees that Bruniaceae tend to occur in mesic microhabitats: south- facing slopes, seeps, marshes, streambanks, and in the shade of boulders. These microhabitats, together with the leaf xeromorphy of the family, may explain how the relatively primitive woods that Bruniaceae have can persist in a Mediterranean-type climate (Carlquist, 1978a). Small leaf surfaces minimize transpiration, but are adaptive because of the sunny climate and lack of shade- offering trees in localities where Bruniaceae grow. However, the leaves of Bruniaceae are not uniform, and this diversity can be related to the diversity of habitats in which species of the family are found. Features of leaf structure have been explored by various authors, notably Colozza (1904), Kirchner (1904), Marloth (1925)' and Niedenzu & Harms (1930). The present account amplifies knowledge of leaves of the family because it is based on liquid-preserved specimens of the majority of species, collected during a visit in 1973. Leaves of dried specimens have supplemented the liquid- preserved specimens. Data from the above-mentioned collections are sufficiently comprehensive to enable distinctions to be made to genus and species concepts within the family. The monograph of Pillans (1947) forms a convenient framework for that comparison. In addition, recent data from wood anatomy (Carlquist, 1978a), cytology (Goldblatt, 1981) and palynology (Hall, 1988) can be incorporated. Leaf anatomy proves to offer more characteristics than one might think interpretable at the level of subfamily or tribe, and the subfamilial groupings offered by Niedenzu & Harms (1930) and Takhtajan (1987) are pertinent in this regard. A few data from leaf anatomy appear to be interpretable with regard to the phylogenetic sequence of genera within the family. Although data from leaf anatomy might be expected to be applicable mostly to infrafamilial taxonomy, a few foliar features seem interpretable at the interfamilial level. Two main lines of relationship have been claimed for Bruniaceae: ericalean (Dahlgren & Van Wyk, 1988) and rosalean (Van Tieghem, 1897; Thome, 1976; Dahlgren, 1980; Cronquist, 1988). Grubbiaceae has been claimed to have various affinities, including ericalean (Fagerlind, 1947; Cronquist, 1988), and this complicates the affinity found by some authors between Bruniaceae and Grubbiaceae (Carlquist, 1977). LEAF ANATOMY OF BRUNIACEAE •; MATERIAL AND METHODS Liquid-preserved leaves were embedded in paraffin and sectioned according to the usual techniques. Dried leaves were treated overnight with warm 2.5% aqueous NaOH, stored in aqueous 50% ethyl alcohol, and then embedded and sectioned as with liquid-preserved specimens. Both transections and paradermal sections were cut for all species. Sections were stained with a safranin fast green combination. Some mesophyll cells stain very deeply because of dense contents of tannins or another, possibly terpenoid, compound, or both. These sections are opaque to a large extent, and do not photograph well. Nevertheless, sections have been illustrated photographically here in order to show accurately the nature of these accumulations. Leaves of most species were examined by means of scanning electron microscopy (SEM). Dried leaves were coated with gold and examined with an ISI WB-6 SEM. Coverage of the family is extensive, considering that 21 species are listed as critically rare, threatened or extinct (Hall & Veldhuis, 1985). Material of some species was not available. Berzelia (12 species) is less well-covered because preliminary investigations showed it to be more uniform; species in that genus and in Brunia were selected for study on the basis of texture and shape diversity. The monograph of Pillans (1947) has been followed with certain exceptions. Author citations are listed in Table 1. Lonchosloma esterhuyseniae was added by Strid (1968) and Tittmannia esterhuyseniae was named by Powrie (1969). On the advice of E. Powrie and of E. Esterhuysen (personal communication), I have differed from the treatment of Pillans (1947) in certain nomenclatural matters. Linconia deusla Pillans is considered a synonym of L. cuspidata. In Slaavia, S. pinifolia is considered the correct name for S. dregeana Presl; S. capilella is considered correct for S. comosa Colozza, and S. trichotoma Pillans is a synonym of S. capilella. Berzelia squarrosa is considered a valid segregate of B. arachnoidea. My collections are represented in the herbarium of the Rancho Santa Ana Botanic Garden (replicates distributed to numerous other herbaria). Collections of other workers are located in the Compton Herbarium of Kirstenbosch Botanic Garden. Length measurements in Table I are taken from Pillans (1947) or from actual specimens and are given to the nearest 0.5 mm. Width and thickness measurements are given to the nearest 0.01 mm, and are taken from microscope slides. All quantitative data in Table 1 represent conditions judged to be typical, but in no instance was sampling that could lead to statistical significance undertaken. Nevertheless, contrasts sufficiently extreme to possess significance are claimed in the data presented. Genera and species are arranged alphabetically in both Table 1 and in the plates. ANATOMICAL DESCRIPTIONS Leaf tip The entire family Bruniaceae is characterized by distinctive brownish apices termed apiculae here. Metcalfe & Chalk (1950) and Dahlgren & Van Wyk TABLE 1. Leaf characteristics of Bruniaccac Character k Species Collection 1 2 3 1 5 6 7 8 9 10 U 12 13 14 15 16 Auduuima capitata Brongniart Carlquist 4460 5.5 0.80 0.41 4 'i 1 5 4- + St K 7 a 2.2 0.17 Berzelia abrolanoides Brongniart CarUpdsi 4478 3.0 1.14 0.52 10 10 2 3 + + s !< 1 in 1.7 0.09 B. arachnuidea F.cklon & Zeyher Carlquist 4646 12.0 0.90 0.70 9 5 2 2 5 + + s K 5 in 5.4 0.68 B. comma lata Sunder Carlquist 4736 5.0 0.53 0.36 5 7 1 6 + + S R 4 a 1.3 0.11 B. cordifolia Schlectendal Carlquist 4690 7.1) 4.50 0.73 6 0 1 6 + 4- S R 18 A 15.8 1.32 B. ecklonis Pillans CarUpdsi 4963 4.5 0.92 0.51 3 6 1 4 +- i- s R 5 .i 2.1 0.23 B. matron Pillans Estnhuysen 4984 6.5 0.89 0.43 11 14 1 4 + + s R 5 a 2.9 0.12 B. rubra Schlechtendal Carlquist 4967 11.0 1.40 0.63 16 18 1 9 + + s DR 7 a 7.7 0.23 B. squarrosa Thunberg Carlquist 4945 7.0 0.87 0.56 11 11 1 4 4- + s R 6 a 3.0 0.14 Bruma albiflora Phillips Carlquist 4576 11.0 0.60 0.33 7 7 1 4 + + s R 3 a 3.3 0.24 n B.