Distribution and Function of Resins and Glandular Hairs in Western Australian Plants by B

16.-Distribution and function of resins and glandular hairs in Western Australian plants by B. Dell' Manuscript received 22 June 1976; accepted 19 October 1976 Abstract of fresh, preserved and in some cases, dried The taxonomic distribution of glandular hairs and resins is documented. Resinous plants herbarium material, were examined and types of are prevalent in some genera within the trichomes and their distribution recorded. The Mimosaceae, Euphorbiaceae, Sapindaceae, results are summarized in Table 1 and a few Boraginaceae, Dlcrastylidaceae, Lamiaceae, Myoporaceae, Solanaceae, and Goodeniaceae. of the trichome types are illustrated in Fig, 1. With few exceptions there is a correlation It is apparent that the majority of resinous between surface resin and glandular hair dis genera are either woody or herbaceous dicoty tribution. The genus Eremophila is discussed as representative of a resinous, arid genus. Son1e ledons. Nearly all plants with external resinous properties of the leaf resins of Beyeria viscosa exudations bear glandular hairs beneath the and Eremophila fraseri are discussed in detail. exudate. It can be assumed that the glandular Resins may have a function in reducing water loss by increasing resistance to cuticular trans hairs in these species are implemented at least piration and by reducing leaf temperature by in resin secretion and perhaps also in resin increasing radiation reflectance from the leaf. synthesis. Exceptions include some taxa of the Myrtaceae, Celastraceae, Fabaceae, Poaceae and Introduction Haemodoraceae. The secretion sites of sticky A systematic treatment of glandular hairs and exudates in some species of Calytrix, Pileanthus, leaf resins in Western Australian plants has not Psammomoya and Burtonia need to be investi been attempted previously. Interest in resin gated further. There is a possibility that epi formation in some species (Dell and McComb dermal cells have a glandular function in these 1975) and the possibility that plant resins may genera. be of use in difficult taxonomic groups (Dell Not all plants with glandular hairs secrete 1975) led to an investigation of the relationship resins (Table ll : some glandular hairs are pig between glandular hairs and surface leaf resins. mented (e.g. Diplopeltis), others produce volatile The significance of resins in plants has oils (e.g. Anthocercis), mucilages etc. In some remained an enigma, proposed functions having plants glandular hairs are confined to the little experimental proof. In Beyeria viscosa the inflorescences (e.g. members of the Proteaceae) ; distribution of the resin on the leaf surface in others the trichomes are confined to the varies according to leaf maturity and is closely leaves, phyllodes and stems (e.g. Acacia) or may tied to the early stages of glandular hair forma occur on both the leaves and the flowers (e.g. tion (Dell and McComb 1974). Incidental Eremophila, Stylidium). observations that this pattern of resin distri Western Australian plants with resinous sheets bution could be altered by temperatures not are prevalent in some genera within the lethal to some plants, led the author to evaluate Mimosaceae, Euphorbiaceae, Sapindaceae, Bora the possible importance of the resin in increas ginaceae, Dicrastylidaceae, Lamiaceae, Myopor ing reflectance of light from the leaves. Pearman aceae, Solanaceae and Goodeniaceae. U966) has indicated the importance of surface The genus Eremophila is an example that features such as hairs and scales in increasing illustrates the prevalence of resinous species in reflectance. Slatyer (1964) and Waggoner 0966) dry habitats. Approximately 70% of the species have noted that the possession of shiny leaf occur in Western Australia where they are most surfaces could probably reduce the heat load abundant in the north and interior regions of by 10-15% under stress conditions. This factor the State. About 43% of these have resinous together with the high heat resistance of some leaves and stems. The resin may exist as a Western Australian plants (e.g. up to 59'C., continuous varnish over the leaves (e.g, E. Grieve and Hellmuth 1968) could be of impor fraseri, E. serrulata), be confined to one surface tance to plants subject to irregular and often (e.g. E. latrobei), or exist as isolated patches Prolonged droughts. (e.g. E. angustijolia, E. duttonii). This variation is reflected in the amount of resin expressed as Distribution of glandular hairs and resins a percentage of leaf dry weight in Table 2. Collections of plants bearing resins and/ or Species with high resin yields usually have con glandular hairs were made in the field. Voucher tinuous sheets of resin, at least on the young specimens are housed in the University of West leaves. ern Australia (UWA) (see Appendix D. Sections Surface resins in all Eremophila species are produced by glandular hairs. The nearly uni 'School of Environmental and Life Sciences, Murdoch versal glandular hair has a short stalk with up _ University, Murdoch, Western Australia, 6153. to eight cells in the head. Many of the species Journal of the Royal Society of Western Australia, Vol. 59, Part 4, June, 1977. 119 Table 1 which do not appear resinous, for example Occurrence and taxonomic distribution of glandular hairs and resinous species with a dense tomentum of stellate or plants in fVestern Australia. Voucher specimens are cited in Appendix I. branched hairs, also have an understorey of Family Examples Distribution of / Surface stalked glandular hairs (Fig. 1). Large branched glandular hairs features* hairs with some glandular tips are scattered Poaceae .. Triodia ? resinous through the tomentum of similar but non Orchidaceae Elythranthera leaves and stems glandular trichomes of E. leucophylla and E. Caladenia inflorescences turtonii. Liliaceae Agrostocrinum inflorescences Haemodoraceae Conostylis ? resinous leaf edges Distribution of resin on the leaf surface Proteaceae Adenantlzos inflorescences viscid Grevillea inflorescences viscid Whilst observing Beyeria leaves under bright Chenopodiaceae Chenopodium leaves and stems lights it was noticed that the surface of the Nyctaginaceae Boerhm'ia leaves and stems Gyrostemonoacea e Didynlotheca leaves and stems resinous leaf changed from matt-like to mirror-like in Capparaceae Cleome leaves, stems, and viscid appearance <Fig.2). It was possible to see reflec inflorescences tion of images from the mirror surface. Leaves Droseraceae Drosera leaves and stems specialized for insect continued to grow after this transformation and ivory presumably were not affected internally by the Byblidaceae Byblis leaves and stems specialized additional radiant heat. When heated in an for insect ivory oven it was found that at 55°C. the abaxial Mimosaceae Acacia young leaves .. viscid, sheet of resin coalesces within two minutes. At resinous 51 °C, the youngest leaves form a sheet in about Caesalpiniaceae.. Cassia rare on leaves Fabaceae ? Genus leaves, stems and resinous the same time but the half-expanded leaves inflorescences take up to flve minutes to achieve the same Burtonia ? resinous resin flow. Twelve minutes exposure at 44 ,C. Tremandraceae Tetratlzeca . rare on young stems causes the resin to run on young and mature Euphorbiaceae Bertya leaves and stems resinous leaves as at the higher temperatures. Resin, Beyeria leaves and stems resinous Ricinocarpos leaves and stems viscid removed from the leaf surface, melts at about Celastraceae Psammomoya ? resinous 48°C, to form a thick, viscous liquid. stems Sapindaceae Dip/ope/tis . mainly inflores- The effect of radiant heat on the leaf surface cences causes the resin to become mobile and, on the Dodonaea leaves and stems resinous younger leaves, the resin flows together on the Malvaceae Abutilon leaves and stems Hibiscus leaves and stems rarely viscid abaxial surface and forms a continuous sheet Myrtaceae Eucalyptus . rare on leaves ? with a smooth surface. On mature leaves the Calytrix ? viscid resin droplets are widely spaced and the effect of Pileanthus ? viscid Plumbaginaceae Plumbago inflorescences, ±viscid heat causes the resin to coalesce into 'rivers'. fruits The composition of the resin on the leaf sur Boraginaceae Halgania leaves and stems resinous Dicrastylidaceae Chloanthes .. leaves and stems face is probably determined by genetic factors Cyanostegia leaves and stems resinous whereas the amount of resin on the leaf surface Dicrastylis .. leaves and stems Laclmostachys leaves and stems is a combination of genetic and environmental Newcastelia leaves and stems viscid, factors and is closely related to the distribution resinous and abundance of g·landular hairs. The distri Pityrodia leaves and stems Avicenniaceae Avicennia leaves and stems specialized bution of the resin on the leaf surface is depend for salt ent on such factors as resin composition, amount secretion of resin/unit area and surface topography. Lamiaceae Hemigenia. leaves and stems Prostantllera leaves and stems resinous If the resin is of adaptive value to the plant, Solanaceae Anthocercis leaves and stems resinous it might be expected that plants growing under Nicotiana leaves, stems and viscid inflorescences some stress conditions would produce more Scrophulariaceae Gratia/a leaves and stems viscid glandular hairs and hence more resin than Stemodia leaves and stems viscid plants growing under mesophytic conditions. Verbascum. leaves, stems and inflorescences New shoots of plants transferred from the fleld Veronica rare on leaves to glasshouses were always softer and

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