OPCE-STR.vp Acta Bot. Croat. 69 (1), 65–70, 2010 CODEN: ABCRA 25 ISSN 0365–0588 Achene surface features in Potentilla subarenaria Borbás ex Zimmeter and P. intermedia L. non Wahlenb. (Rosaceae) JEREMI KO£ODZIEJEK University of £ódŸ, Department of Geobotany and Plant Ecology, Banacha 12/16, 90-237 £ódŸ, Poland Achenes morphology in Potentilla L., i.e. P. subarenaria Borbás ex Zimmeter and P. intermedia L. non Wahlenb. was examined with stereoscope and scanning electron micro- scope (SEM). Achenes of these taxa varied in shape, size, colour, the surface sculpture and in the dimensions of dorsal ridge and ribs. SEM analyses allowed distinguishing two morphological types of seed coats pattern: ruminate-reticulate sculpture due to well pre- served epidermal cells in P. subarenaria and tuberculate sculpture in P. intermedia. The main taxonomic features of these two taxa are: the microstructure, size, shape and colour of achenes. Key words: Rosaceae, Potentilla, achenes, SEM Introduction Fruit in Potentilla L. named also achene is dry, not dehiscent and monospermous, small in size. Morphological description of achenes of selected species from the genus Potentilla were given by many authors before: CLARK and FLETCHER (1909), BRESINSKY (1963), ROUSI (1965), OCKENDON and WALTERS (1970), WERNER and SOULE (1976), LEHT (1989), SOJÁK (1987, 1993), ANDENBERG (1994), KO£ODZIEJEK and GABARA (2007). Within this ge- nus, KELLEY (1953) described the fruit morphology for 11 taxa and included a key for their determination, WERNER and SOULE (1976) described it in 3 taxa, ANDERBERG (1994) in 28 taxa, LEHT (1989) in 24 taxa. However, among these authors, only LEHT (1989), KO£O- DZIEJEK and GABARA (2007) presented SEM analysis of selected taxa of Potentilla. It is known that fruit and seeds are very useful in identification and classification of plant taxa (MURLEY 1951, KARCZ 1996, KO£ODZIEJEK and GABARA 2007, ÖZCAN 2004, FAGÚNDEZ and IZCO 2004). Description of achenes in P. subarenaria and P. intermedia is limited to their length, shape and colour (WOLF 1908, JUZEPCZUK 1941, KELLEY 1953, SZAFER and PAW£OWSKI 1955, SOJÁK 1995). These features, however, are not sufficient to identify species. Nobody has studied achenes of P. intermedia and P. subarenaria based on scanning electron microscope (SEM); only ANDENBERG (1994) examined both species ACTA BOT. CROAT. 69 (1), 2010 65 * Corresponding author, e-mail: kolo@biol.uni.lodz.pl U:\ACTA BOTANICA\Acta-Botan 1-10\Kolodziejek1.vp 9. travanj 2010 12:37:08 Color profile: Disabled Composite 150 lpi at 45 degrees based on light microscopy (LM). This author described achenes of this taxa as medium in size between 0.8–1.3 mm long, 0.7–0.9 mm wide and 0.4–0.6 mm thick and medium buff and orange-brown in colour. Many European authors consider P. intermedia as hybridogenous species, with P. argentea L. and P. norvegica, or even other allied species, as the parents. P. subarenaria is commonly interpreted as an apomictic species possibly of relatively recent hybrid origin from P. tabernaemontani Ascherson and P. incana P. Gaertner, B. Meyer et Scherb. (KURTTO et al. 2004). The aim of the study is to present a morphological analysis of achenes in two Potentilla species using a scanning electron microscope (SEM) and to estimate the usefulness of shape, size and fruit surface for the taxonomy of investigated species. Materials and methods Nomenclature of Potentilla subarenaria Borbás ex Zimmeter and P. intermedia L. non Wahlenb. was used according to WOLF (1908). Plant material was obtained from natural populations collected by the author in the area of Poland. Analysis of qualitative and quantitative characteristics was performed on ripe, fully de- veloped achenes. Some achenes, even at the ripe stage, are distinctly smaller than typical ones and are also deformed – such achenes were deformed and distinctly smaller than typi- cal ones and such achens were not measured. Colour of the achenes was determined in the day light on the basis of colour scale rec- ommended by BERGGREN (1969). Dimensions – length, width and thickness of the achenes, width of the aril and width and height of dorsal ridge were measured according to the de- scription presented in figure 1. Morphometric analysis of the achenes, except aril and rib 66 ACTA BOT. CROAT. 69 (1), 2010 KO£ODZIEJEK J. Fig. 1. Achene of Potentilla sp.: ventral (A) and lateral (B) view. 1 – length, 2 – width, 3 – thickness, 4 – dorsal ridge, 5 – aril around scare attachment, 6 – style scare. U:\ACTA BOTANICA\Acta-Botan 1-10\Kolodziejek1.vp 9. travanj 2010 12:37:10 Color profile: Disabled Composite 150 lpi at 45 degrees dimensions, was made by a stereomicroscope Nikon SMZ 800. At least 30 achenes from five plants were analyzed for each taxon. For scanning electron microscopy (SEM) samples were mounted on metal stubs, sput- tered with technical gold (Pelco S.C 6 coating system), examined and photographed using a Tesla BS 340 scanning electron microscope. Shape of achenes, dimensions of aril and ribs as well as the seed surface pattern were analyzed on 5 photographs for each taxon. The carpological documentation includes SEM figures which represent: outline of the achenes from the lateral side and the seed surface structure from the central part of the lateral sur- face. Results Achenes in subarenaria and P. intermedia are bilateral, shape ovate, laterally flattened, apex obtuse, curved, base obtuse (Fig. 2). Fruit thickness measured in a straight line per- pendicular to the symmetry plane ranges from 0.61 (± 0.02) mm in P. subarenaria to 0.85 (± 0.02) mm in P. intermedia. The shape of fruit is described to some extent also by the elongation and flattening coefficients given in table 1. Achenes are elongated, i.e. from 1.19 (P. intermedia) to 2.04 (P. subarenaria) times longer than wide. Flattening of the achenes is usually bilateral, rarely the achenes are ± equally thick as wide. The most flat- tened are achenes of P. subarenaria (width/thickness ratio = 1.31), the least flattened ones – the achenes of P. intermedia (ratio = 1.18). Two types of achenes are distinguished: large, present in P. subarenaria and small, present in P. intermedia (Tab. 1). Achene colour varies from red-brown in P. intermedia to nut-brown in P. subarenaria. Scare attachment, i.e. the point of achene attachment to the receptacle is surrounded by an aril slightly visible in P. subarenaria or clearly – in P. intermedia, with their respective widths being 20 mm and 40 mm (Tab. 2). A clear dorsal ridge about 40 mm wide and 40 mm thick was present in achenes of P. intermedia (Tab. 2), while unclear one, about 10 mm wide and 10 mm thick was observed in P. subarenaria (Fig. 2A left). Ribs seen at achenes surfaces are brown in colour (Tab. 1). Distinct ribs, very sharp in shape were seen in achenes of P. intermedia (Figs. 2A, B right), or oval in shape – in P. subarenaria (Figs 2A, B left). Width of ribs varied from 20 mm in P. subarenaria up to 80 mm in P. intermedia (Tab. 2). Similarly rib height was the lowest (20 mm) in P. subarenaria, while the largest (40–60 mm) was in P. intermedia. ACTA BOT. CROAT. 69 (1), 2010 67 ACHENE SURFACE FEATURES IN POTENTILLA Tab. 1. Colour and dimension of achenes (in mm) in taxons of P. subarenaria Borbás ex Zimmeter and P. intermedia L. non Wahlenb. Taxon Lengh Width Thicknes Lengh/ width Width/ thicknes Colour achenes ribs P. intermedia 1.19±0.02 1.00±0.02 0.85±0.02 1.19±0.02 1.18±0.02 red-brown pale P. subarenaria 1.63±0.01 0.80±0.01 0.61±0.02 2.04±0.02 1.31±0.02 nut-brown brown U:\ACTA BOTANICA\Acta-Botan 1-10\Kolodziejek1.vp 9. travanj 2010 12:37:10 Color profile: Disabled Composite 150 lpi at 45 degrees 68 ACTA BOT. CROAT. 69 (1), 2010 KO£ODZIEJEK J. Tab. 2. Characteristics of achenes in Potentilla subarenaria Borbás ex Zimmeter and P. intermedia L. non Wahlenb. (SEM). Taxon Aril Dorsal ridge Surface sculpture Ribs (mm)Width Width Thickness mm mm Width Heigth P. intermedia conspicuous 40 conspicuous 80 40 tuberculate 80 40–60 P. subarenaria iconspicuous 20 incons- picuous 10 10 ruminate- reticulate 20 20 Fig. 2. Surface sculpture of the achenes of Potentilla subarenaria Borbás ex Zimmeter (left A, B, C figures) and P. intermedia L. non Wahlenb. (right A, B, C figures), at different magnifica- tions; ´200 (A), ´1000 (B) and ´3000 (C). Arrow indicates dorsal ridge. U:\ACTA BOTANICA\Acta-Botan 1-10\Kolodziejek1.vp 9. travanj 2010 12:37:11 Color profile: Disabled Composite 150 lpi at 45 degrees Based on the features of the arrangement of cells and cell outline, two types of seed coats pattern were identified: – ruminate-reticulate sculpture; among distinct and sharp ribs well preserved epidermal cells, hexagonal in shape were visible. Seed coats of this type were characteristic of P. subarenaria (Figs 2B, C left); – tuberculate sculpture, characterized by wrinkles and ridges irregular, most of them running in one direction. This type of seed coats was typical for P. intermedia (Figs 2B, C right). Discussion Scanning electron microscopic analysis of achenes from P. subarenaria and P. inter- media allowed to distinguish new additional features such as aril, dorsal ridge and aril di- mensions, useful in taxonomy of this taxa. These features of achenes in addition to the mor- phology of leaves (WOLF 1908, JUZEPCZUK 1941, BALL et al. 1968, SOJÁK 1995) proved to be of high systematic importance in taxonomy of Potentilla species. The most useful diag- nostic characteristic in determination of P. subarenaria and P. intermedia is surface sculp- ture. My investigations in taxa from Potentilla L., i.e. P. subarenaria and P. intermedia. re- vealed differences in colour and shape of achenes, as well as in their sizes. According to my measurements the lengths of achenes P. intermedia, 1.19 mm, were similar to those de- scribed by SOJÁK (1995) and ANDENBERG (1994), 0.8–1.3 mm. The identification of immature achenes is hardly practical. Many of the species whose achenes are prominently ridged or wrinkled when mature are completely smooth when young. On the other hand, the style scar is more likely to be easily located in young achenes, and in many species the style may still persist. Sites and collection of P. subarenaria and P. intermedia: P. subarenaria – Œl¹sk prov., Góry Towarne hills near Kusiêta village (Wy¿yna Czêstochowska upland) 50°45’N/19°16’E, xerothermic grassland; P. intermedia – £ódŸ prov., Nowosolna village near £ódŸ 51°42’N/19°37’E, gravel-pit; Œl¹sk prov., Olsztyn village near Czêstochowa (Wy¿yna Czêstochowska upland) 50°46’N/ 19°16’E, roadside. Acknowledgement The author would like to thank Dr Krzysztof Polañski (Institute of Physics, University of £ódŸ) for taking the photographs. References ANDENBERG, A. L., 1994: Atlas of seeds and small fruits of northwest-European plant spe- cies with morphological descriptions. Resedaceae-Umbelliferae 4, 1–281. Swedish Museum of Natural History, Stockholm. 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