Biodiv. Res. Conserv. 16: 1-106, 2009 BRC www.brc.amu.edu.pl 10.2478/v10119-009-0022-2 Variation in seed morphology in the genus Erica L. (Ericaceae) Piotr Szkudlarz Department of Plant Taxonomy, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 PoznaÒ, Poland, e-mail: [email protected] Abstract: Seed morphology was studied in 136 species of Erica, including 123 from South Africa (Cape Floristic Region), 5 from tropical Africa, and 8 from Europe. Seed anatomy was studied in 13 selected species by light and scanning electron microscopy. Seed morphology of each species was described and documented by SEM micrographs. Ten major diagnostic features were selected, concerning seed shape, primary sculpture, and fine relief. On the basis of these features, the species were divided into 14 groups. Within them, 40 morphologically homogeneous subgroups were distinguished, which could possibly be used in future revisions of the genus. A key to species identification has been developed on the basis of seed characteristics. A very close similarity was observed between seeds of some Erica species from distant parts of the distribution range of this genus. Key words: Erica, carpology, seed sculpture, fine relief, seed coat, cluster analysis, Cape Floristic Region Contents 1. Introduction ............................................................................................................. 2 2. Morphology and geographic range of the genus ..................................................... 4 3. Material and methods .............................................................................................. 5 4. Results ..................................................................................................................... 8 4.1. Seed structure in the genus Erica .................................................................. 8 4.2. Seed morphology and general characteristics of the species ........................ 11 4.3. Key to identification of Erica seeds ............................................................. 79 4.4. Morphological seed variation in the genus Erica ......................................... 83 4.5. Phenetic analysis based on seed morphology in Erica ................................. 86 5. Discussion ............................................................................................................... 89 References .................................................................................................................... 92 Appendix. Seeds of Erica photographed in the light microscope ................................ 95 VARIABILITY, AND VARIABILITY, TAXONOMY PHYLOGENY © Adam Mickiewicz University in PoznaÒ (Poland), Department of Plant Taxonomy. All rights reserved. 2 Piotr Szkudlarz Variation in seed morphology in the genus Erica L. (Ericaceae) 1. Introduction South African Erica spp. and related genera was con- ducted by E. G. H. Oliver and I. M. Oliver. On the basis Erica is one of the major genera of the family of herbarium specimens and field research, they described Ericaceae. The number and rank of taxa distinguished a few dozen new species (Oliver 1967, 1984, 1985, within this genus vary depending on classification. 1986, 1990, 1993b; Oliver & Oliver 1991, 1995a, Currently about 865 species are included in this genus 1995b, 1996a, 1996b, 1997, 1999a, 1999b, 1999c, (Oliver 2000). According to this classification, it is the 2000a, 2000b, 2000c, 2000d, 2001a, 2001b, 2002b, largest genus of the Ericaceae, larger even than the genus 2002c, 2004; Oliver et al. 1997; Turner & Oliver 2006). Rhododendron (Stevens et al. 2004), which is commonly Those studies formed a basis for numerous revisions of believed to include the largest number of species. Erica spp. and of allied genera, so-called minor genera The generic name Erica comes from the Old Greek (Oliver 1976, 1980, 1987a, 1987b, 1988, 1993a, 1994). word ereika, which was used by Theophrastus. Carl E.G.H. Oliver finally suggested that all minor genera Linnaeus, in his fundamental work Species Plantarum should be included in the large genus Erica (Oliver (1753), described this genus on the basis of 23 species, 2000). One of the major effects of the research is yet including 12 from South Africa. Intensive research in another complete revision of this genus, presented in the Cape Region resulted in the description of new Erica parts (Oliver & Oliver 2002a, 2005). Those authors, in spp. Carl Thunberg greatly contributed to the knowledge general, preserve Guthrie and Bolusís (1905) division of this genus. On the basis of field research and a rich into sections, but they emphasize that the presented clas- herbarium collection, he described many new species sification of this genus is still far from satisfactory. They (Thunberg 1785). Another major step in research on note also that the available morphological characters this genus was a work written by Richard Salisbury are not sufficient to determine a natural system of clas- (1802), which presented results of his analysis of her- sification and that this requires a molecular phylogeny. barium specimens from numerous collectors. On the As shown by examples of research conducted in basis of a revision of all the available material, he other systematic groups, fruits and seeds provide good recognised 236 species. He created the basis for the diagnostic features (Barthlott & Voit 1979; Barthlott division of the genus into sections and subsections, 1981). However, in spite of great progress in carpo- which were later used by Don (1834) and Bentham logical studies and general recognition of the high value (1839). In the 1820s, German collectors also started field of carpological characters, the family Ericaceae has not research in South Africa, and supplied numerous her- been sufficiently investigated in this respect (Stevens barium specimens, e.g. to Berlin. These collections 1971; Oliver 1991, 2000). Earlier studies concerned, as formed a basis for research on the Ericaceae conducted a rule, only single taxa or small groups of species by Klotzsch (1838). He included Erica spp. and closely (Artopoeus 1903; Beijerinck 1940; Gleisberg 1922; related species in a taxonomic group called Ericearum, Niedenzu 1890; Winton 1902), which could not give a and within it he distinguished tribes and numerous gen- full picture of fruit and seed diversity. era. At the same time, this plant family was studied also Plants of the genus Erica, like other members of the by George Bentham (1839). In contrast to Klotzschís Ericaceae, have ovules with a single integument, i.e. classification, Benthamís (1839) concept of the genus both their ovules and seeds are unitegmic (Artopoeus Erica was very clear, based on well-defined principles, 1903; Netolitzky 1926; Peltrisot 1904; Corner 1976; primarily on stamen structure. He divided the genus into Takhtajan 1992). The nucellus, lying under the integu- 4 subgenera and 49 sections. Another important step in ment, is used up during embryo-sac development, so research on Erica spp. was Guthrie and Bolusís (1905) the seeds are described as tenuinucellate. The endosperm work. They suggested a new classification of the ge- is composed of thin-walled cells. It is nuclear in this nus, based on corolla and calyx structure, and distin- plant family, except for the genus Rhododendron, where guished 5 subgenera divided into 41 sections. This publi- endosperm is cellular (Corner 1976). It contains well- cation for many years was the basis of the classifica- defined haustoria, both micropylar and chalazal; in ripe tion of this genus. It should be noted, however, that it is seeds they are inactive, lignified and deformed (Takhta- concerned only with taxa from the former Cape Province, jan 1992). The embryo is relatively large, straight, com- so it does not cover the whole genus. Salterís (1950) posed of 2 cotyledons, hypocotyl, and radicle. It is flora of Cape Peninsula included 100 species of Erica. located at the centre of the endosperm oriented longitu- For the whole Cape Province, the genus was next re- dinally, occupying º to æ of its length. Its radicle is orien- vised by Dulfer (1965), who verified many synonyms ted towards the micropyle (Corner 1976; Takhtajan and added species described after 1905. In total, he listed 1992; Szkudlarz 2001). The thin integument is com- 605 species of Erica but generally preserved the classi- posed of only 4-10 layers of cells (Netolitzky 1926; fication and numbering of species by Guthrie & Bolus Corner 1976; Takhtajan 1992). The seed coat develops (1905). In the last few decades, intensive research on from the outer part of the integument, i.e. from its epi- Biodiv. Res. Conserv. 16: 1-106, 2009 3 dermis, so the seeds are described as exotestal. During his numerous works on new species he includes infor- seed development, other layers of the testa are resorbed mation about the size of seed and character of seed coat or compressed. As a result, mature seeds of Erica are (Oliver 1986, 1987, 1990; Oliver & Oliver 1991, 1995, surrounded by a seed coat composed of only a single 1997, 1999a, 1999b, 1999c, 2000a, 2000b, 2000c, layer of cells as a rule (Szkudlarz 2001, 2006). 2000d, 2001a, 2001b, 2001c, 2001d, 2002a, 2002b, In recent decades, scanning electron microscopy 2004; Oliver et al. 1997; Turner & Oliver 2006; Dorr (SEM) has gained particular importance in research on & Oliver 1999). Moreover, also Fraga (1984) and seed morphology, showing that seed characters have a Fag˙ndez & Izco (2003a, 2003b, 2004a,