Potentilla L.
Cinquefoil.
Rosaceae, rose family.
Vegetative morphology. Plants perennial herbs. Taproot present. Caudex present. Vegetative, aerial, stem a small transition zone between roots and basal leaves, or vegetative stem a small transition zone between roots and branches arising at ground-level. Leaves in a basal tuft; alternate; compound; existing for a single season or less, or marcescent. Stipules present; scale-like; green. Stipules hairy. Petioles (3–)5–40(–80) mm long.
Reproductive morphology. Flowering stems present. Calyx sepals free; (2–)3–7(–8) mm long. Calyx green, or brown; hairy. Petals free; 5; yellow; 2–10(–12) mm long; (3–)4–8(–9) mm wide. Stamens 15–30; filaments glabrous. Anthers yellow; ellipsoid, or triangular; 0.2–0.8 mm long. Gynoecia superior. Carpels 25–45. Styles conical, or straight; basal portion smooth, or covered with short papillae, less than 0.1 mm high, or covered with long papillae, 0.1 mm high or higher. Stigmas broad-cylindrical, or plate shaped, or capitate. Fruit sessile. Fruit with calyx persisting; dry; an aggregate of nutlets; ovoid. Fruit green at maturity, or straw coloured.
Distribution. Northern hemisphere distribution: Greenland, St. Pierre and Miquelon, Canada, United States, Eurasia.
Notes. Potentilla species known from the Arctic Islands fall
into three groups (genera or subgenera). Two of these are taxonomically
uncomplicated; genus Comarum L. (subgenus Comarum (L.) Syme with
Comarum palustre) and Argentina Lam. (subgenus
Chenopotentilla (Focke) Juz. with Argentina egedii). These are not
very closely related to the third group (or to each other). Their species are
most probably sexual and do not, as far as known, form hybrids. The third group,
Potentilla L. s.s (subgenus Hypargyrium Fourr.), has three
sections in the Arctic: sect. Aureae (Th. Wolf) Juz. with P.
crantzii and P. hyparctica, sect. Multifidae (Rydb.) Juz. with
P. pulchella, and sect. Niveae (Rydb.) Juz. with at least three
species of the P. nivea complex and two of the P. uniflora
complex. All these seem to be facultative to nearly obligate agamosperms (see
Asker and Jerling 1992, Eriksen 1996, Nyléhn unpubl.), even if the
evidence is scanty for some of them. Pseudogamy seems to be the rule and one of
the most common outward signs of agamospermy, nearly perfect fruit/seed-set, is
therefore absent also in the agamosperms. Pseudogamy requires pollination for
endosperm development but the pollen does not fertilise the ovule. Pseudogamy
may occur with pollen from the same species or from a related species which is
often more efficient (Nyléhn personal communication). Predominance of
agamospermy has recently been shown (Nyléhn unpubl.) in the three
Svalbard taxa of the P. nivea complex: P. nivea, P.
hookeriana subsp. chamissonis, and the local P. insularis
Soják, which is possibly conspecific with P. rubricaulis s.l. The
variation pattern found in P. pulchella (see Hansen et al. 2000) and in
other parts of sect. Multifidae also indicates at least some degree of
agamospermy.
Both species concept and species delimitation are problematic
in agamospermous plant groups. Soják (1985, 1986, 1989) interpreted the
complicated morphological variation found in these sections of Potentilla
to be the result of extensive hybridisation between 'primary' species both
within and between sections. Hybrids could then propagate, form populations, and
even attain ranges, by agamospermy. Entities assumed to be such stabilised
agamospermic hybrids have been treated as species by Soják (1985, 1986,
1989). This approach was also adapted by Yurtsev (1984, 1999 in draft) for the
arctic flora and has resulted in about 60 species being named from the arctic or
near arctic areas. More than half of these species are considered to have
resulted from hybridization. One of the basic assumptions in the approach of
Soják and Yurtsev is that digitate and subpinnate leaves in these groups
are a result of hybridisation between 'primary' species with ternate (i.e.,
sect. Niveae and parts of Aureae) and truly pinnate leaves (sect.
Multifidae).
Four hybrid species have been reported by Soják
and Yurtsev from the arctic areas surrounding the North Atlantic. In three of
these hybrid species Soják's hybrid origin hypotheses have been shown to
be improbable.
1. Potentilla scandica Soják - interpreted by
Soják as P. crantzii x P. gelida C.A. Meyer - represents
rather normal variation in leaflet number in P. crantzii (Nyléhn
personal communication) see below.
2. Potentilla subquinata (or P.
nivea subsp. subquinata) - interpreted by Soják as P.
nivea s.s x P. pulchella - is genetically different from P.
nivea s.s from Scandinavia (Nyléhn 1999) but does not include genetic
markers from P. pulchella (Hansen et al. 2000, Hamre 2000, Nyléhn
in prep.). It is rather a part (race) of P. nivea.
3. Potentilla
insularis - interpreted by Soják as P. hookeriana subsp.
chamissonis x P. lyngei - is only found in areas where P.
lyngei (from sect. Multifidae) is absent and does not include genetic
markers from P. pulchella which is the Multifidae species present
in the area (Svalbard, see Hansen et al. 2000, Hamre 2000). It might be better
interpreted as a locally deviating part of a more widely delimited species or
species group which also includes the western hemisphere arctic expression of
P. rubricaulis.
4. The fourth hybrid species reported by
Soják, P. protea Soják - interpreted as P. crantzii
x P. hyparctica - seems to be only single, first-generation hybrid
plants, from the material investigated from northwestern Russia, Svalbard,
Greenland, and Canada (Elven unpubl.).
Yurtsev (1999 in draft) reports the
following hybridogenous taxa from the eastern Canadian Arctic and/or
neighbouring parts of Greenland: P. nubilans Soják ined. (P.
hookeriana subsp. chamissonis x P. hyparctica), P.
pedersenii (Potentilla sect. Niveae x P. pulchella),
P. protea, and P. subquinata (see above).
A few specimens in
the material investigated from the Arctic Archipelago (CAN, DAO, O) seem to
represent several hybrid combinations.
P. hookeriana coll. x
hyparctica (1–2 sites on Baffin, one site on each of Ellesmere,
Victoria, and Banks),
P. hookeriana subsp. chamissonis x
nivea (two sites on Baffin),
P. hookeriana coll. x
pulchella (one site on each of Devon, Ellesmere, and Banks),
P.
hookeriana subsp. hookeriana x rubricaulis s.l. (two sites on
Ellesmere, one on Banks),
P. hyparctica x nivea (one site on
Baffin),
P. hyparctica x pulchella (one site on each of
Baffin, Devon, and Melville),
P. hyparctica x rubricaulis s.l.
(possibly one site on Baffin),
P. nivea x rubricaulis s. lat.
(one site on Baffin),
P. pulchella x rubricaulis s. lat. (two
sites on Banks),
P. vahliana and another parent (two specimens from
Baffin, one from each of Axel Heiberg and Melville).
Some of these hybrid
products may form local populations, as there are several individual plants
collected from some of the sites, but none of them seem to be more than local
phenomena that do not deserve special rank.
The complicated taxonomy and
nomenclature of Soják and Yurtsev is based on a specific hybridisation
model. This model has proved insufficient for explaining the investigated North
Atlantic supposedly 'hybrid' taxa; it is not needed to explain the variation
found in the material from the Arctic Islands either. The supposition that there
is an inherent, and very important, taxonomic difference between ternate,
digitate and pinnate leaves has proved erroneous because transitions between
leaf types occur very easily with changing growth conditions (Eriksen and
Nyléhn 1999, Hamre 2000). Until further evidence is produced the taxonomy
and nomenclature is based on the morphological and genetic evidence available.
This results in a fairly traditional taxonomy with broadly delimited species,
very close to that of Porsild (1955). It is evident that hybridisation occurs
occasionally, especially with the prevalence of pseudogamy. It is also probable
that such hybrid offspring may propagate by agamospermy and produce deviating
populations, and population groups. However, it remains unproved that any of the
generally accepted and widespread taxa in the Arctic Islands have a hybrid
origin and the naming of single hybrids, hybrid populations or even population
groups should be dissuaded.
A note about hairs and glands. - The
kinds of hairs and their location, have been, and still are, decisive for
species definition and delimitation in many parts of the genus. This is
specially the case within the complicated sect. Niveae and related
groups. The following categories are found and used in the descriptions where
relevant. Some further discussion of hairs and their importance is found in
Eriksen and Yurtsev (1999) and the concepts and descriptions below are based on
their proposals.
Floccose hairs - are flat, irregularly twisted or
felted and more or less appressed to the surface. The hairs are usually so long
and intertwined that it is impossible to tell where a single hair begins or
ends. They often form a dense tomentum on the lower leaf surface and petiole but
may also occur scattered on the peduncle and inflorescences axes. Among our
species, such hairs characterize P. nivea and its hybrids. They are
easily discernible with a strong lens or a dissection microscope.
Crispate hairs - are unicellular, and less than 1 mm long. The more
or less individual hairs are terete, wavy often in a corkscrew-like fashion.
They may form a tomentum on the lower leaf surface or the petiole and sometimes
they make the peduncle appear villous. Among our species, such hairs
characterize P. pulchella, P. rubricaulis s.l., P.
uniflora, and P. vahliana.
Straight or nearly straight
hairs - appear in several shapes and may be smooth or verrucose ('rough').
To decide unambiguously between smooth and verrucose one needs a very strong
magnification (SEM, Scanning Electron Microscopy) but it is possible to get an
impression, with a little training, using a strong dissecting microscope. The
surface of smooth hairs appears even and often shiny, that of verrucose hairs
slightly irregular and a little dull due to impeded translucence.
Straight, smooth, long, and sub-appressed to spreading hairs - form a
silky indumentum ('long-silky') that characterizes petioles, leaf surfaces, and
partly peduncles in P. uniflora, P. vahliana and P.
pulchella. Similar hairs, that are verrucose, characterize P.
rubricaulis s.l. This type of indumentum appears soft as opposed to the
next.
Strongly spreading to patent, long, straight hairs -
characterize P. crantzii, P. hyparctica, and P. hookeriana
s.l. Those of P. crantzii are smooth, those of P. hyparctica
smooth or verrucose, and those of P. hookeriana s.l. are verrucose and
especially stiff ('bristly').
Glands occur in most of the species, both as
sessile glands on most plant parts and as glandular hairs on petioles,
peduncles, and leaves. Potentilla crantzii and P. hyparctica are
heavily glandular, the others less so. Thus, the number and distribution of
glands seem to be potentially of less taxonomic importance than the hairs (see
Eriksen and Yurtsev 2000).
Cite this publication as: ‘S.G. Aiken, M.J. Dallwitz, L.L. Consaul, C.L. McJannet, L.J. Gillespie, R.L. Boles, G.W. Argus, J.M. Gillett, P.J. Scott, R. Elven, M.C. LeBlanc, A.K. Brysting and H. Solstad. 1999 onwards. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 29th April 2003. http://www.mun.ca/biology/delta/arcticf/’. Dallwitz (1980) and Dallwitz, Paine and Zurcher (1993, 1995, 2000) should also be cited (see References).