Trichome Morphology Provides Phylogenetically Informative Characters for Tremandra, Platytheca and Tetratheca (Former Tremandraceae)
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Trichome morphology provides phylogenetically informative characters for Tremandra, Platytheca and Tetratheca (former Tremandraceae) Trisha L. DowningAC, Pauline Y. LadigesA, and Marco F. DurettoBD ASchool of Botany, The University of Melbourne, Parkville, Vic. 3010, Australia BTasmanian Herbarium, Tasmanian Museum and Art Gallery, Private Bag 4, Hobart, Tas. 7001, Australia C National Herbarium of Victoria, Royal Botanic Gardens Melbourne, Birdwood Ave., South Yarra, Vic. 3141, Australia. DCorresponding author: [email protected] This paper was published in Plant Systematics and Evolution 271: 199-221 (2008) (published online 21 March 2008). Abstract. Trichomes of Tremandra R.Br. ex DC., Platytheca Steetz and Tetratheca Sm. (Elaeocarpaceae, former Tremandraceae), together with two outgroup species of Elaeocarpus L., are illustrated using Scanning Electron Microscopy, and their distribution on various plant organs is documented. Various trichomes types were identified that relate taxa: simple hairs, stellate hairs, short glandular trichomes, long glandular trichomes, and three forms of tubercules. Both outgroup and ingroup taxa have simple hairs. Stellate hairs are confirmed as unique to Tremandra. Prominent and sculptured multi-celled tubercules, some bearing a stout hair, are characteristic of Platytheca. Smaller multicelled tubercules occur in both Platytheca and Tetratheca, except for the Western Australian taxon Te. filiformis (possibly plesiomorphic). Unicellular tubercules (papilla) characterise two species of Tetratheca. Short glandular trichomes, usually found on the ovary, also occur in both of these genera but not in all species (possibly secondary losses), while long glandular trichomes, usually on stems and leaves, occur only in some groups of Tetratheca. Within Tetratheca, Western Australian taxa that have five-merous flowers fall into three ‘groups’: seven species (together with one from South Australia) that have short glandular trichomes but no long glandular trichomes; six species that have long glandular trichomes but no short glandular trichomes; and four species that have both trichome types. All other species of Tetratheca have four-merous flowers and form two ‘groups’: twelve eastern species (including one from South Australia) that have both short glandular trichomes and long glandular trichomes; four western species and six eastern species that lack short glandular trichomes. Based on these characters, a phylogenetic hypothesis for the three genera is presented. Keywords: Tremandra, Platytheca, Tetratheca, Elaeocarpaceae, trichomes, scanning electron microscopy, phylogeny Introduction Oligocene-Miocene with the onset of greater aridity in Australia. Molecular studies, Tremandraceae are a small family of three including exemplar taxa, indicated that genera endemic to temperate regions of Tremandraceae is sister to (Savolainen et al. Australia, predominantly in the southern 2000a, b), or nested within (Soltis et al. 2000; regions of the mainland and Tasmania (Fig. 1). Crayn and Rossetto 2003; Crayn et al. 2006) Crayn et al. (2006) concluded that the genera Elaeocarpaceae. Some recent classifications are a dry-adapted clade, related to rainforest have formally sunk Tremandraceae into taxa within Elaeocarpaceae, that dates back to Elaeocarpaceae (APG 2003, Coode 2004), but the Paleocene but radiated during the the group is considered monophyletic. 1 (1845, 1853), Schuchardt (1853), Bentham (1863) and Thompson (1976). Thompson’s revision (1976) recognised 39 species of Tetratheca, and was the basis of the most recent flora accounts of the family for Australia: Victoria (Jeanes 1999), New South Wales (Gardner and Murray 1992; Carolin and Tindale 1993), Queensland (Stanley and Ross 1983), South Australia (Stove 1986), and Western Australia (Wheeler 1987; Grieve 1998; Wheeler et al. 2002). Since Thompson's revision an additional six species have been described (Alford 1995; Butcher and Sage 2005; Butcher 2007) and there are still several undescribed species in south-western Western Australia (Butcher 2007; Western Australian Fig. 1. Distribution of the tremandroid clade Herbarium 2007). Also, Te. procumbens (Elaeocarpaceae, formerly Tremandraceae). Hook.f., which Thompson (1976) reduced to synonymy under Te. pilosa Labill., was reinstated by Jeanes (1996), and Te. elliptica The three genera of the former Joy Thomps. is now considered to be a Tremandraceae (hereafter called the synonym of Te. setigera Endl. (Western tremandroid clade) are Tremandra R.Br. ex Australian Herbarium 2007). Tetratheca DC., Platytheca Steetz and Tetratheca Sm., currently contains 45 described species. including 49 species. Species are small Tetratheca occurs in both eastern and western perennial shrubs, ranging from almost mainland Australia as well as Tasmania; prostrate alpine plants to shrubs not much however, no species is found on both sides of more than one metre in height, and the the continent. The group, with its high majority are localised endemics. Stamens frequency of regional endemics (Butcher et al. open by a terminal pore, situated adjacent to 2007), has the potential to contribute to the anther in Tremandra or surmounting an knowledge of the biogeographic history of anther tube of varied length and colour in regions in south-western and eastern Australia. Platytheca and Tetratheca, except in Te. Since the time of Steetz (1845), various gunnii (Thompson 1976). attempts have been made to divide Tetratheca Tremandra is characterised by the into tribes and sections based on characters presence of stellate hairs and includes only such as stamens, seeds, ovules, leaf form and two species, Tr. stelligera R.Br. and Tr. indumentum; none has been satisfactory. diffusa DC., both of which are endemic to Comparative documentation of morphological south-western Western Australia. Platytheca characters of all taxa is required for also includes only two species, characterised phylogenetic analysis, since molecular data by verticillate leaves and an inner whorl of may not be fully informative (Crayn and anthers that are broader and longer than the McPherson pers comm.). There have been outer whorl. Both species are endemic to some anatomical studies, based on only a southwestern Western Australia, with P. limited number of species, of wood (Carlquist galioides Steetz widespread (a distribution 1977), flowers (Saunders 1939; Suvartha et al. similar to Tremandra) and P. juniperina 1984; Laxmi and Narayana 1987; Rani 1995; Domin a narrow endemic, known from few, Matthews and Endress 2002), pollen (Erdtman scattered populations. 1972; Johri et al. 1972), ovules and seeds (van Tetratheca is the largest of the three Tiegham 1906; Berg 1975; Corner 1976; genera, with a combination of characters but Biddle and Christophel 1978; Boesewinkel no clear synapomorphy. Major taxonomic 1999). Thompson (1976) and Butcher (2007) works on Tetratheca include those by Steetz noted that the type and/or combination of 2 trichomes present, of which Thompson (1976) Material was preserved either using recognised six types, are important characters 70% Ethanol or by air-drying. Specimens for identification of species within Tetratheca; preserved in 70% ethanol were dehydrated these trichomes, however, have yet to be though a graded ethanol series and then critical documented in detail for potential use in point dried. All samples were mounted on phylogenetic analyses. aluminum SEM stubs using double-sided Our aim was to define and illustrate the carbon tabs and coated with gold using an characteristic trichome-types of these taxa Edward’s S150B Sputter Coater. The samples using scanning electron microscopy, and were viewed and photographed using a Philips document their distribution, combination and XL30 Field Emission Scanning Electron abundance on both vegetative and Microscope (FE SEM). One image, of a fruit reproductive organs. of E. holopetalus (see Fig. 13a), was captured using a Leica DC 300F digital camera. The Materials and methods camera was mounted on a Leica MZ FLIII Dissector Stereo Light Microscope using a A total of 16 species, covering the three 0.63x adaptor. genera, Platytheca, Tremandra and Tetratheca, was examined using scanning electron microscopy (SEM). These species Results were selected to ensure that all trichome types were illustrated and that representative taxa Trichome types. Trichomes observed by SEM from across the geographic range of the genera were divided into the following categories: were sampled. Two outgroup species of stellate hairs (Fig. 2), simple hairs (Fig. 3), Elaeocarpus L., E. holopetalus F.Muell. and short glandular trichomes (Fig. 4), long E. reticulatus Sm., were also studied, glandular trichomes (Fig. 5) and three types of representing members of the sister clade tubercules (Fig. 6). Trichome types are identified by Crayn et al. (2006). Details of considered to be independent characters since specimens and material examined for the SEM they can occur in combination on a particular study are given in Table 1. In addition, all 49 plant (Table 2). species of the tremandroid clade, with the Stellate hairs (Fig. 2), with four to exception of four recently described and rare eight rays, were only observed in Tremandra, Western Australian species (Butcher and Sage in both species. They occur on various organs, 2005; Butcher 2007) and Te. fasciculata Joy including leaves, stem (Fig. 2a), surface of the Thomps., for which there was insufficient capsule (Fig. 2b), pedicel (Fig. 2c), ovary and material