Image of Potentilla pusilla Host

Description:

Slo.: pritlini petoprstnik - , syn.: Potentilla puberula Kraan, Potentilla gaudinii Gremli, Potentilla cinerea, P. verna L., subsp. puberula (Kraan) Hegi, P. glandulifera Kraan - Habitat: former stony pasture; old overgrown scree, slightly southeast inclined slope; calcareous ground; dry, nutrients poor, shallow soil layer, among low grasses and mosses; sunny place, exposed to direct rain, average precipitations ~ 3.000 mm/year, average temperature 7-9 deg C, elevation 610 m (2.000 feet), alpine phytogeographical region. - Substratum: soil. - Comment: Potentilla pusilla is a Middle and South European plant growing in almost all parts of Alps and one of almost 30 species of this genus growing in Slovenia (and one of about 500 worldwide). It is an example of species, which is not easy to determine. Ref.:(3) frankly states that distinguishing it from other species, which also belong to Potentilla verna aggregate is not clear and even contradictory described in literature. To make the situation worse for an amateur the determination depends on very small and sparse plant's hairs. All dichotomous keys of genus Potentilla known to me split genus Potentilla already in a fairly early stage of determination process into two groups of plants - with and without stellar hairs. If one makes a wrong decision with respect to existence and type of these hairs the result of determination is a failure. All references state that Potentilla pusilla should have stellar hairs. Unfortunately, the authors don't agree where these hairs should be located. Ref.: (2) states 'on the whole plant', Ref.: (3) states 'at least at leaf margins', Ref.:(4) assumes they are 'on the upper and lower surface of the leafs', Ref.:(6) states 'on margins and lower and upper surface of leafs' and Ref.:(7) claims they can be found on the lower side of leafs only. Additional difficulty is the fact that these hairs are expected to be not only sparse but also very small and unevenly distributed. Although I looked for them, I haven't found them even with my good quality 10x magnifier and therefore never came to an acceptable determination of the plants photographed. Only after I was instructed to check thoroughly Potentilla pusilla traits again and I put the plant under a dissecting microscope I found these stellar hairs and hence recognized the plant. The hairs were really small and sparse. Interestingly, I noticed two types of them (in addition to vast majority of other types of hairs). The hairs of the first type are located on the lower side of the leaf surface. They are very sparse and maximally 100 m long, most of them much shorter, and without much larger central hair. Hairs of the second type are easier to find and are located here and there at the margins of leafs. They are surrounding the base of much larger (> 20 times), simple, up to 1(2) mm longleaf side hairs. Most of the second type stellar hairs are shorter than 50 m. I was unable to find stellar hairs on the upper side of leafs, leaf petioles and other parts of the plant. This 'hair picture' doesn't fit fully to any of species description known to me. But, since these hairs appear to be a very variable trait of this species, I still believe the determination is correct. Plants were growing in groups, sometimes forming quite large flat 'cushions' with many beautiful flowers. - Ref.: (1) Personal communication with Dr. Igor Dakskobler, SAZU, Natural History Institute Jovan Hadi. (2) K. Lauber and G. Wagner, Flora Helvetica, 5. Auflage, Haupt (2012), p 262. (3) M.A. Fischer, W. Adler, K. Oswald, Exkursionsflora sterreich Liechtenstein, Sdtirol, LO Landesmuseen, Linz, Austria (2005), p 484. (4) A. Martini et all., Mala Flora Slovenije, Tehnina Zaloba Slovenije (2007) (in Slovene), p 254. (5) D. Aeschimann, K. Lauber, D.M. Moser, J.P. Theurillat, Flora Alpina, Vol. 1., Haupt (2004), p 774. (6) Rothmaler 3, Exkursionsflora von Deutschland, 11. Aufl., Elsevier, Spectrum (2007), p 237. (7) H. Haeupler, T. Muer, Bildatlas der Farn- und Bltenpflazen Deutschlands, Ulmer (2000), p 219.