Potentilla L.
(incl. Duchesnea Smith; excl. Comarum L., Dasiphora Rafin., Drymocallis Rydberg, Fragaria L.)
Potentilla is a large genus that mainly occurs in the northern hemisphere. Depending on its generic delimitation it includes ca. 300 to more than 500 species. In its traditional circumscription (e.g. Wolf 1908) it is not monophyletic and the generic limits of Potentilla are still very controversial. The present account is in accordance with recent molecular phylogenetic research by Potter & al. (2007) and considerably differs from traditional taxonomic concepts within this genus (cf. Lambinon & al. 2012 for Belgium). Subtribe Fragariinae appears to be well-delimited from Potentilleae. In fact, the latter only includes Potentilla s.str. (incl. Duchesnea). Alchemilla L. (incl. Aphanes L.), Dasiphora, Drymocallis and Fragaria belong to Fragariinae and are accepted as distinct genera. Dobeš & Paule (2010), on the contrary, – also based on molecular phylogenetic studies – suggested to accept Potentilla in a very wide sense, as to include, among others, Alchemilla, Aphanes, Comarum, Dasiphora, Fragaria, etc. (see also: Mabberley 2008, Christenhusz & Väre 2012). According to Töpel & al. (2011) many questions about the phylogenetic relationships in the genus have not yet been answered. Even within Potentilla as accepted here generic limits remain unclear. According to Soják (2010) Argentina Hill. is a distinct genus: styles are subterminal and especially stipules have ventral auricles (lateral in Potentilla s.str.). These morphological differences seem to be confirmed by (some) molecular studies (e.g. Dobeš & Paule 2010). This segregate genus includes, among others, native Argentina anserina (L.) Rydb. (Potentilla anserina L.) and related species.
In Belgium the following species are believed to be native: Potentilla anglica Laichard, P. anserina L., P. argentea L., P. erecta (L.) Rauschel, P. reptans L., P. sterilis (L.) Garcke, P. supina L. and P. tabernaemontani Aschers. (Lambinon & Verloove 2012). Some of these also occur as introductions in areas where they are not originally native (usually in heavily disturbed habitats). Native Potentilla rupestris L. is now accommodated in a segregate genus (as Drymocallis rupestris (L.) Soják).
Several species of Potentilla are cultivated as ornamentals. Leslie & Walters (1995) and Jäger & al. (2008) provide useful overviews of the genus in cultivation in Europe. A peculiar cultivar of native Potentilla reptans L., f. pleniflora Bergmans, has been recorded as an established escape in a disused railway siding near Torhout since 2012.
Potentilla s.str. is a taxonomically very complex genus. Many species are apomictic and some are presumably of hybrid origin. In Belgium identification problems are mostly encountered within sections Rivales and Argenteae. Typical plants of all species are easily distinguished but fully fertile, intermediate plants sometimes occur. Most critical appears to be the separation of (native) Potentilla argentea s.l., P. inclinata and P. intermedia s.l. (incl. P. heidenreichii Zimm.). See under these species for a thorough discussion. Potentilla argentea itself is a variable species and in fact consists of a polyploid complex of apomictic and sexual microtaxa (see Kurtto & al. 2004 for an interesting discussion and numerous references). Potentilla neglecta Baumg., one of these microspecies, characterized by leaflets that are grey-green above with 9-11 acute teeth and slightly larger petals (5-7 mm vs. 4-5 mm) (Ball & al. 1968), occurs in large parts of Europe and is possibly overlooked, either as a native taxon or as an introduction. See also Paule & al. (2011). Likewise, records of native Potentilla supina may include related, non-native subspecies. These are mostly distinguished on achene characters (outline and ornamentation; see Soják 1987 for additional information, also: Kurtto & al. 2004). At least the Asian subsp. costata Soják has been recorded in Europe (for instance in Bamberg in Germany, see: http://www.flora-deutschlands.de/images/potentilla%20.jpg).
1 Corolla deep-rose or crimson === Potentilla nepalensis
Corolla yellow or white === 2
2 Corolla white === 3
Corolla yellow === 4
3 Leaflets oblong-obovate, crenate-dentate near apex only (entire in lower 2/3). Petals 6-9 mm, obviously longer than sepals === P. montana
Leaflets broadly obovate, +/- crenate-serrate throughout. Petals ca. 5 mm, as long as to slightly longer than sepals (native) === P. sterilis
4 Lower leaves pinnately divided (native) === P. anserina and P. supina
Lower leaves ternately to palmately divided === 5
5 Petals and sepals in all or at least some flowers 4 (native) === P. anglica and P. erecta
Petals and sepals always 5 === 6
6 Flowers solitary in the leaf axils. Stem procumbent, usually rooting at the nodes === 7
Flowers in few- to many-flowered, terminal or (rarely) lateral cymes. Erect to procumbent === 8
7 Leaves ternate. Receptacle becoming red and succulent in fruit. Epicalyx segments 3-toothed at apex === P. indica
Leaves palmate with 5 leaflets. Receptacle remaining dry in fruit. Epicalyx segments entire at apex (native) === P. reptans
8 Slender procumbent perennial, rooting at the nodes (mat-forming). Flowering cymes lateral (native) === P. tabernaemontani
Erect annual, biennial or perennial, never mat-forming. Flowering cymes terminal === 9
9 Lower side of leaflets densely white-tomentose (indumentum entirely obscuring the leaf surface), indumentum of short, crispate hairs. Leaf margins inrolled (native) === P. argentea
Lower side of leaflets not densely white-tomentose, subglabrous to densely pubescent (if more or less obscuring leaf surface, than indumentum greyish and of short, crispate hairs and longer patent hairs). Leaf margins flat === 10
10 Petals minute, 1-2 mm long (ca. ½ as long as sepals). Anthers usually 5-10. Mature achenes smooth === P. rivalis
Petals larger, at least 4 mm (slightly shorter to distinctly longer than sepals). Anthers always 10 or more. Mature achenes ridged === 11
11 Most leaves ternate. Calyx distinctly accrescent at maturity === P. norvegica
Most leaves palmate, with 5-7 leaflets. Calyx not accrescent at maturity === 12
12 Petals distinctly longer than sepals, 6-12 mm long, mostly (very) pale yellow. Leaflets 5-7 === P. recta
Petals +/- equaling sepals, 4-9 mm long, pure yellow. Leaflets 5 === 13
13 Petals 5-9 mm long. Anthers 0,5-1,3 mm long. Lower side of leaflets usually with +/- surface obscuring indumentum of short crispate hairs and long patent hairs (especially on the veins). Leaflets evenly toothed, with 5-9 teeth on either side (reminiscent to those of P. recta) === P. inclinata
Petals 4-5 mm long. Anthers 0,3-0,5 mm long. Lowerside of leaflets very variable, ranging from subglabrous to densely hairy (sometimes nearly obscuring leaf surface), indumentum of long patent hairs. Leaflets irregularly toothed, often with fewer teeth === P. intermedia
Literature:
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