Scanning Electron Microscopy of the Leaf Epicuticular Waxes of the Genus Gethyllis L

Soulh Afnc.1n Journal 01 Bol811Y 2001 67 333-343 Copynghl €I NISC Ply LId Pnmed In South Alnca - All ngills leserved SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254- 5299 Scanning electron microscopy of the leaf epicuticular waxes of the genus Gethyllis L. (Amaryllidaceae) and prospects for a further subdivision C Weiglin Technische Universitat Berlin, Herbarium BTU, Sekr. FR I- I, Franklinstrasse 28-29, 0-10587 Berlin, Germany e-mail: [email protected] Recei ved 23 August 2000, accepled in revised form 19 January 2001 The leaf epicuticular wax ultrastructure of 32 species of ridged rodlets is conspicuous and is interpreted as the genus Gethyllis are for the first time investigated being convergent. In three species wax dimorphism was and discussed. Non-entire platelets were observed in discovered, six species show a somewhat rosette-like 12 species, entire platelets with transitions to granules orientation of non-entire or entire platelets and in four in seven species, membranous platelets in nine species a tendency to parallel orientation of non-entire species and smooth layers in eight species, Only or entire platelets was evident. It seems that Gethyllis, GethyJlis transkarooica is distinguished by its trans from its wax morphology, is highly diverse and versely ridged rodlets. The occurrence of transversely deserves further subdivision. Introduction The outer epidermal cell walls of nearly all land plants are gle species among larger taxa, cu ltivated plants , varieties covered by a cuticle cons isting mainly of cutin, an insoluble and mutants (Juniper 1960, Leigh and Matthews 1963, Hall lipid pOlyester of substituted aliphatic acids and long chain et al. 1965, Hallam 1970, Rentschler 1974, Baker 1974, primary and secondary alcohols (HOlloway 1982). The cuti 1982, Reed and Tukey 1982) and must therefore be taken cles of the majority of seed plants are covered with epicutic into account (Meusel et al. 1994). On the other hand, envi ular wax secretions in the form of wax layers and crusts or ronmental influences and modifications of epicuticular wax epicu ticular crystallOids or bolh (surveys in Martin and ultrastructure were observed. Alt hough these influences Juniper 1970, Barthlott and Wollenweber 1981 , Cutler et al. could alter Ihe degree 01 the wax depOSits (Irom either very 1982, Jeffree 1986, Barthlolt et al. 1998) . dense 10 less dense or lotally absent) or its chemical com Since Ihe lirst SEM-sludies were published (Amelunxen et position (Juniper 1960, Hall et al. 1965, Hallam 1970, Bake r al. 1967), il became evident thai epicuticu lar wax crystalloid 1974, Rentschler 1974, Reed and Tukey 1982), only in rare types are a relevant systematic and taxonomic character cases is the crystalloid type itself changed (Baker 1982). (Barth loti and WOllenweber 1981, Jeffree 1986, Frolich and Therefore, in most cases the ultrastructure of epicuticular Barthlott 1988 , Barthlott 1990, 1994, Barthlott and Theisen wax crystalloids has been shown to be a Significant system 1998, Barthlolt et al. 1998). It has been shown Ihat the atic character in higher and lower level taxonomy (JeHree respective type of epicuticular waxes (and other cuticular 1986, Engel and Barthlott 1988, Fehrenbach and Barthlott sculpturing) is geneticallY determined (Culler and Brandham 1988, Fr61ich and Barthlott 1988, Barthlott 1990, 1994, 1977, Barthlott and WOllenweber 1981 , Cutler 1982) and is Hennig et al. 1994, Theisen and Barthlott 1994, Ditsch et al. often specific for a taxon at different levels: a genus (i. e. 1995, Wilhelmi and Barthlott 1997, Barthlott and Theisen Eucalyptus l. Heritier: Hall am and Chambers 1970, 1998, Barthlott et al. 1998). Nelumbo Adans.: Barth lott et al. 1996), a family (i.e. Gethyllis L. possesses some un iq ue features which are Poaceae: Baum et al. 1980, Tulloch 1981, Fabaceae: Ditsch exceptional within the Amaryllidaceae. II is Ihe only genus et al. 1995) or higher taxonomic groups (Fr6lich and where 6, 12, 18 or more stamens (sometimes connate), a Barthlott 1988, Hennig et al. 1994, Ditsch and Barthlott spiral arrangement of leaves and, together with Apodolir;on, 1997). a subterranean ovary occur (Dahlgren, Clifford and Yeo Some environmental influences and infraspecific varia 1985, Meerow 1995, MUller-Dobl ies an d Muller-Doblies tions in the structure and development of epicuticular waxes 1996, Meerow and Snijman 1998, Snijman 2000). From a (Juniper 1960, Leigh and Matthews 1963, Hall et al. 1965 , systematic viewpoint Gethyllis is usuallY allied to the tribe Hallam 1970, Rentschler 1974, Baker 1974, 1982) and con Haemantheae which possessses many supposed primitive ve rgent shapes of waxes based on different chemical com fealures (Bjorn stad and Friis 1972). Its exact pOSition , how position. however, can sometimes occur mainly in some sin- ever, is slill under discussion. Dahlgren, Clifford et al. (1985) 334 considered Gethyllis (and Apodalirian Baker) as possibly Results being re lated to the basal tribe Haemantheae while Meerow (1995) assigned it to this tribe. Muller-Doblies and Muller The main wax types found in the genus Gethyllis are Doblies (1996) and Meerow and Snijman (1998) placed it in described briefly in section A using the te rminology of the tribe Gethyllideae. In an updated phylogenetic analysis Barthlott et al. (1998) and are illustrated in Figures 1-12. In of the Amaryllidaceae, however, the tribe Gethyllideae finds section B the species are listed in alphabetical order and , no molecular support (Meerow et al. 1999). whenever a characteristic pattern or assembly of the ir wax Since the first revision of the genus by Baker (1885) who type is present, it is described in greater detail. In Table 2 the recognised nine species , new species were added until investigated species are su mmarised according to their 1933 and later by Muller-Doblies (1986) so that, today, it respective wax types . Unless otherwise stated, no differ comprises about 32 species all located in the winter rain fall ences between upper and lower leaf surfaces were found areas and also the Karoo of southern Africa (Burtt 1970, and the wax crystalloids are non-oriented at the cell surface. Snijman 2000). H Bolus, using a single characte r, was the For description purposes the density of the wax layer was first who attempted to subdivide the genus Gefhyllis inlo the defined as 'loose' (approximately 30- 50 % of the surface vis sections Clinastylis which included species with a long , ible) , 'dense' (10- 30% of the surface visible) and 'very exserted and declined style and Ol1hastylis which included dense' (surface not visible). If two wax types were observed species with a straight and (comparatively) sh ort style on one eel! surface the te rm wax dimorph ism is used. In this (MacOwan and Bolus 188 1). Baker (1885), however, made paper the terms 'platelets' (instead of scales) and 'crystal re fe rence in his monograph to this character in his key, but loids' (instead of crystals / crystallites) are prefe rred (ef. dis failed to mention Ihe section names. Nearly 100 years laler, cussion in Barthlott et al. 1998). A few unpublished names of based on his preliminary investigations, Muller-Doblies species/subspecies were used in the text. To highlight this, (1982, 1986) suggested a further subdivision of Gethyllis, these names were marked wi th parentheses followed by i. e. into two subgenera with ten series (Prof Dr Muller the ir collection numbers. Doblies, pers . comm. ). For systematic and taxonomic pur poses , the epicuticular waxes of 32 species of the genus A, Wax crystalloid types in Gethy/lis Gethyllis L. were studied by high resolution SEM with a view to facilitating a better understanding of the genus. Smooth layers (Figure 1): According to Barthlott et al. Many proposals for the classification of the diHerent wax (1 99S) , continous wax coverings are normally less than 1 ~m crystalloid types have, over a period of time, been published thick and lack any visible surface sculpturing. Species with (De Bary 1871 , Amelunxen et al. 1967, Wilkinson 1979, out wax crystalloids are described by this term in this paper. Barthlott and Wollenweber 1 9S1 , Baker 1 9S2 , Jeffree 19S6). Because no fissures or cracks were observed in any of the The most recent typification by Barthlott et al. (1998) shall species investigated, however, this term is purely specula form the basis lor this presentation. tive . But it can be assumed that the thin wax coverings, hardly detectable in SEM, represent Ihe obligate outermost Materials and Methods border of the cuticle of presumably all land plants (ef. Hallam 1982, Jeffree 1986, Barthlott et al. 1995). Young leaves were harvested from the living collection BTU Granules (Figure 5) : Irregular, mostly isodiametric, ohen (Berlin-Dahlem) (Table 1) and pieces of about 3 square mm rounded crystalloids, ranging from very small to moderately were immediately fixed for 4.5 hours with 2.5% glutaralde large. In th is paper this type is only observed as a transi hyde. The leaves were fixed , infiltrated, and dehydrated tional form to entire platelets (see below). using the glycerol infiltration method described by Ensikat Non-entire (= irregular) platelets (Figu res 2 and 9): Flat and Barthlott (1993). Aher dehydration the samples were crystalloids, more or less irregular in shape and with irregu mounted on commercial SEM-stubs with double-adhesive lar margins, usually 1-10~m high, protruding ± perpendicu tape and stored fo r two weeks or longer in an desiccato r with larly from the

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