IAWA Bulletin n.s., Vol. 8 (2),1987 95 WOOD ANATOMY OF PELARGONIUM (GERANIACEAE) by 1. J.A. van der Walt*, E. Werker** and A. Fahn** * Department of Botany, University of Stellenbosch, Stellenbosch 7600, Sout Africa, and ** Department of Botany, The Hebrcw University of Jerusalem, Jerusalem, Israel Summary The wood anatomy of 12 species of Pelargo­ cally simple but occasional multiperforate plates nium, nine of the section Pelargonium and in Pelargonium; intervascular pitting predomi­ three re1atively woody species of three other nantly alternate; parenchyma paratracheal, sections, is compared. scanty; rays when present heterogeneous and The secondary xylem is described and quan­ very variable in height and cell size; fibres with titative data of the elements are given. The ves­ simple or indistinctly bordered pits, often sep­ sels have simple perforation plates. However, in tate and thin-walled. P. cucullatum subsp. tabulare reticulate plates A valuable contribution towards the knowl­ are also present. Living fibres and septa te fibres edge of the wood anatomy of Pelargonium are found. Both paratracheal and apotracheal came from Arnold (1951) who studied the axial parenchyma are present. The rays are stern of P. zonale (L.) L'Herit. in detail. The heterogeneous, consisting mainly of square and retention of living fibres in the mature wood upright cells. was interpreted by hirn as a new deve10pment Of all the wood characters, those of the rays and not as areversion to a primitive condition. constitute the most valuable taxonomie fea­ According to Arnold (l.c.) the ancestor of P. tures. Wood anatomieal characters confirm that zonale was probably a woody perennial of ar­ the seetion Pelargonium is a natural and a prim­ borescent habit. itive one. A research team at the Department of Bota­ The relationship between the annual rain fall ny, University of Stellenbosch, is currently re­ and features of the vessels is also presented. vising the genus Pelargonium taxonomieally. Key words: Pelargonium, Geraniaceae, wood A multidisciplinary approach is followed where­ anatomy, taxonomy, ecology. by as many characters as possible are used for the delimitation of the taxa and the determina­ Introduction tion of the relationships between the taxa. This Pelargonium L'Herit. is certainly one of the wood anatomical study forms part of the larger best known genera of flowering plants. Culti­ project. vars of this genus are popular garden and pot The seetion Pelargonium is eonsidered to be plants which are grown on a large scale in al­ the most primitive seetion in the genus (V an most all the countries of the world. der Walt, 1985), and one of the objectives of Despite the popularity of the genus, the this wood anatomical study was to search for available information on its anatomy, especially additional evidenee eoncerning the supposed the wood anatomy, is scant. MacDuffie (l92!) phylogenetie position of the seetion. For this and Thompson (1923) no ted the irregular net purpose the wood anatomy of nine species of perforation plates which are sometimes present the section Pelargonium is compared with that in Pelargonium. Heimseh (1942) gave some in­ of three other relatively woody specks of three formation on the wood anatomical features of different sections. The project naturally con­ the Geraniaceae (sensu lato) but he studied on­ tributes to the knowledge of the wood struc­ Iy one species of Pelargonium. Metcalfe and ture of the Geraniaceae, and characters of Chalk (1950) summarised the literature relating taxonomie value are identified. to the anatomy of the Geraniaceae (sensu lato) that has appeared since the publication of Sole­ Material and Methods reder's Systematic Anatomy of Dieotyledons Stern segments of eomparable lateral branches in 1908, and they gave the following synopsis of at least five years old and a diameter of c. 25 of the wood anatomical features of the family: mm were collected in the fjeld and fixed in vessels solitary and in multiples and clusters; F AA. In the case of P. abrotani/olium and P. sometimes ring-porous; perforation plates typi- grandij10rum the thiekest main sterns available Downloaded from Brill.com09/27/2021 10:26:42PM via free access 96 IAWA Bulletin n.s., Vol. 8 (2),1987 Table I. Material studied. Section Stellen- Collector and l.ocality Grid Average bosch number reference annual project rainfall Species number (mm) (STEU) Seetion Pelargonium P. citronellum J.J.A. v.d. Walt 2707 v.d. Walt 1120 Ladismith 3321 AD 350 3010 v.d. Walt 1296 Garcia's Pass 3321 CC 443 P. eurollatum (L.) L'Herit. 545 v.d. Walt 470 Cape Town 3318 CD 577 subsp. tabulare Voischenk 1943 v.d. Walt 934 Simonstown 3418 AB 558 P. glutinosum (Jacq.) L'Herit. 2700 v.d. Walt 1113 Ladismith 3321 AD 350 3009 v.d. Walt 1295 Garcia's Pass 3321 CC 443 P. graveoIens L'Herit. 1261 v.d. Walt 690 Grahamstown 3326 AD 684 3437 v.d. Walt 1485 Soutpansberg 2329 AB 680 P. greytonense J.J.A. v.d. Walt 1415 v.d. Walt 708 Greyton 3419 BA 619 3377 v.d. Walt 1481 Riviersonderend 3419 BB 427 P. hispidum (L. f.) Willd. 2708 v.d. Walt 1121 Ladismith 3321 AD 350 3615 v.d. Walt 1512 Saron 3319 AA 518 P. papilionaeeum (L.) L'Herit. 1645 v.d. Walt 827 Swellendam 3320 DC 725 3028 v.d. Walt 1315 Greyton 3419 BA 619 P. seabrum (L.) L'Herit. 1073 v.d. Walt 630 Ladismith 3321 AD 350 3361 v.d. Walt 1472 Piquetberg 3128 DD 480 P. vitifolium (L.) L'Herit. 573 v.d. Walt 499 Stellenbosch 3318 DD 704 3034 v.d. Walt& Somerset West 3418 BB 935 Vorster 1321 Section Ligularia P. abrotanifolium (L. f.) Jacq. 681 Moffett 1019 Graaff-Reinet 3224 BC 345 2434 v.d. Walt 1053 Worcester 3319 CB 240 Seetion Eumorpha P. grandiflorum (Andr.) Willd. 3613 v.d. Walt 1510 Saron 3319 AA 518 3622 v.d. Walt 1514 Tulbagh 3319 AC 460 ~ction Cieonium P. zonale (L.) L'Herit. 1370 Ward s.n. Grahamstown 3326 AD 684 3623 v.d. Walt 1515 Tulbagh 3319 AC 460 (c. 10-20 mm) were collected. Herbarium Wood sections of 15-30 Jlm were made with vouchers of all the material collected are housed a Reichert sliding microtome without any pre- in the Department of Botany, University of ceding treatment of the fixed material. The sec- Stellenbosch (STEU). Of each species, material tions were stained with a mixture of Safranin 0 of two locaIities was collected and studied and Alcian green (Joe!, 1983). Macerations were (Table I). prepared with Jeffrey's fluid and stained with Downloaded from Brill.com09/27/2021 10:26:42PM via free access IAWA Bulletin n.s., Vol. 8 (2),1987 97 Safranin O. Thick sections of some species were ferent lengths are present. Vessel members with studied with a Jeol JSM-35 scanning electron two terminal/sub terminal perforation plates as microscope after they had been coated with well as a lateral one, are not uncommon. gold. Inter-vessel pils. - The shape of the apertures Quantitative da ta shown in Table 2 are based of the bordered pits varies from slit-like to el­ on 25 measurements/counts per collection for liptic (Fig. 5), and the lateral waU pitting varies each of the characters. In cases of big infraspe­ from scalariform to opposite to alternate (Figs. cific differences (e. g., number of vessels per 3 & 5). AU three types of pitting may occur in square mm), an additional 25 measurements/ the same vessel member. The pits at the ends of counts per collection were made to verify the the vessel members are often horizontally elon­ results. The data were collected from the peri­ gated and the pitting consequently scalariform. pheral wood - the secondary xylem formed Vessel grouping. - The vessels of all the spe­ during the first two years was excluded. eies are grouped in radial multiples or clusters with a low percentage of the vessels occurring solitary (Fig. 6). The radial multiples may con­ Results sist of 2-30 vessels but there are usually less A synopsis of the anatomical data of the 12 than 10 vessels. The clusters may consist of 3- speeies studied is shown in Table 2. The speeies 20 vessels although seldom more than 12. are arranged according to the average annual Distribution of vessels. - The secondary xy­ rainfall figures, starting with P. abrotanifolium lem of all the species is diffuse-porous (Fig. 7), from the most xeric habitat (300 mm per an­ although there is a tendency towards semi-ring­ num) and ending with P. vitifolium from the porous wood in P. cucullatum subsp. tabulare, most mesic habitat (825 mm per annum). The P. glutinosum, P. grandiflorum, P. hispidum, P. three species of the other sections are indicated papilionaceum, P. scabrum and P. zonale. This to distinguish them from the nine species of tendency varies within individuals of the same the section Pelargonium. species and could possibly be ascribed to vary­ ing environmental conditions or the sampling Vessels of the wood segments. Vessel shape in transection and wall thick­ Dimensions. - As shown in Table 2, the mean ness. - The vessels appear more or less angular length of the vessel members varies from 145 in transections (Figs. I & 6) and the cell walls J.1.m in P. abrotanifolium to 385 J.1.m in P. vitifo­ are 1.5-3 J.1.m thick. lium. According to a classification in Radford Vessel frequency. - The number of vessels et al. (1974) the vessel members of P. abrotani­ per square mm for each species is given in folium are extremely short and those of P. pa­ Table 2. The highest number of vessels was re­ pilionaceum medium sized.