Pinus mugo

Turra 1765

Common names

Dwarf mountain pine [English], Krivulj, planinski bor [Serbian], Klek [Bulgarian], Klec [Czech], Сосна стланиковая европейская [Russian], Bergkiefer, Krummholzkiefer, Bergföhre [German], Pin des montagnes [French], pino montano, pino mugo [Italian] (Jovanovic 1986, Businský 1998, M.P. Frankis field notes, Bulgaria 1998), sosna kosa, kosodrzewina [Polish].

Taxonomic notes

Pinus mugo and Pinus uncinata have been treated as either two species, or as two subspecies of P. mugo, for most of the past 200 years; there has never been clear agreement on this point. Formerly morphological, and now molecular analyses have established that they are sister species; moreover their natural hybrid, Pinus × rotundata Link (Businský 1998), is common. Recent comprehensive reviews of the conifers by Eckenwalder (2009) and Debreczy and Racz (2011) maintain subspecies status for P. uncinata, while Farjon (2010) grants it species status. In principle I agree that subspecies status is probably more appropriate, but the European literature published in the 21st century almost universally treats P. uncinata as a distinct species, and so it is treated here. There is a complexity resulting from this; many collections of P. mugo have been made without declaring the specimen to be of the "mugo" type or the "uncinata" type; see the map below. In practice, the two taxa are distinguished mainly on the basis of habit; P. mugo is a shrub while P. uncinata is (usually) arborescent.

Christensen (1987) gives a highly detailed synonymy with a nearly three page list of names which have been published (excessive use of names for inconsequential variation is a common problem with European pines); a brief summary of the most significant and commonly seen names is as follows (from Christensen 1987):

Pinus mugo Turra 1765: syn. Pinus mugo subsp. mugo Turra; P. montana Miller; P. mughus Scopoli; P. pumilio Haenke; P. mugo var. pumilio (Haenke) Zenari.

Pinus × rotundata (Link) Janchen & Neumayer: syn. P. rotundata Link; P. humilis Link; P. pseudopumilio (Willk.) Bech; P. obliqua Sauter; P. uliginosa Neumann ex Wimmer.

Hybrids are also recorded frequently with P. sylvestris (P. × rhaetica Brügger), and less often with P. nigra and P. heldreichii.

Description

Shrub 1-3(-5) m tall, with one or more curved trunks; branches long, base laying on the ground (up to 10 m from base), with ± ascending or erect major branch ends; rarely a tree. Bark thin, ash-gray-brown to blackish-grey, splitting in angular scaly plates on old stems. Shoots uninodal, glabrous, greyish-black to deep red-brown grooved between the decurrent scale-leaves. Buds ovoid-conic, 6-9 mm, red-brown, very resinous. Leaves in fascicles of two (rarely three around apical bud of strong shoots), bright to dark green, often with a greyish tinge, straight to slightly twisted, minutely serrulate, 23-75 mm long, 0.9-2.1 mm wide, leaf sheath persistent, grey, 15-18 mm. Leaves persistent (2-)4-9(-10) years. Plants usually monoecious, rarely subdioecious. Male cones 10 mm, yellow or red, pollen shed May to July. Female cones purple ripening matte dark brown in late September to October 15-17 months later and opening then, or (if covered by winter snow first) the following spring; sessile or nearly so, symmetrical, 18-55 mm long, 14-28 mm wide (closed), opening to 25-45 mm, angle of inclination to stem 90°-130°; apophysis thin, flat, flexible, 6-10 mm wide and 1-2 mm thick, rhomboidal with a sharp transverse keel, rarely moderately thickened to pyramidal; umbo central, 3-4 mm wide. Seed black, 3-4 mm with a 7-12 mm wing buff with darker streaks; cotyledons (3-)5-7(-8). Cones shed soon after seed release or up to a year or two later. (Jovanovic 1986, Christensen 1987, M.P. Frankis, field notes and herbarium material, Bulgaria 1998). See García Esteban et al. (2004) for a detailed characterization of the wood anatomy.

Distribution and Ecology

Albania, Austria, Bosnia & Herzegovina, Bulgaria, Croatia, Czechia, France, Germany, Italy, Macedonia, Montenegro, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland, and Ukraine. It grows at altitudes of 1400-2500+m, mostly in the high subalpine region at and above the timberline, but also at lower altitudes in peat bogs and frost hollows, exceptionally as low as 200 m in SE Germany and S Poland (Jovanovic 1986, Christensen 1987). Highest altitudes are reached in the extreme S of its range in the Pirin Mts of SW Bulgaria, where it reaches at least 2700 m (M.P. Frankis field notes and herbarium material, Bulgaria 1998). Although this widespread species is not of conservation concern, P. mugo in Croatia is protected by law. Hardy to Zone 3 (cold hardiness limit between -39.9°C and -34.4°C) (Bannister and Neuner 2001).

Distributions of P. mugo, P. uncinata and their nothospecies P. × rotundata. P. mugo are classified as "P. mugo s.s." which are specimens synonymous with P. mugo subsp. mugo; and "P. mugo s.l." which are specimens that could be assignable to either P. mugo subsp. mugo or P. mugo subsp. uncinata. Due to the large number of records (over 50,000) data have been subsampled to 0.1 degree spatial resolution. Source, GBIF.org (2021.11.12) GBIF occurrence download https://doi.org/10.15468/dl.348a34.

P. mugo is also naturalized in Canada: Alberta, British Columbia, Ontario, and Québec; and the USA: Massachusetts, Michigan, Minnesota, New Hampshire, and Wisconsin (PLANTS database 2009.03.31).

Remarkable Specimens

The oldest known specimen, 283 years, was documented in a tree-ring chronology covering the period 1681-2008 (fully crossdated), collected in Swiss National Park, Grisons, Switzerland by Christof Bigler (doi.org/10.25921/wyqz-ag79). This tree's record ended in 1977, so it was presumably dead; two living trees provided a 255-year record. Only two chronologies have been developed for this species, and older trees likely exist. This site was used in a study of P. mugo mortality (Bigler and Rigling 2013).

Ethnobotany

Used to protect soil against erosion and to retard avalanching. Wood hard, heavy. Needles are the source of oil (Jovanovic 1986), and are also used for a (delicious!) herbal tea in Bulgaria (M.P. Frankis field notes, Bulgaria 1998). As an ornamental it is very popular with rock and landscape gardeners, particularly in Scadinavia, Holland and Germany, where it is widespread in municipal parks and gardens (Businský 1998; M.P. Frankis, pers. obs.). USDA hardiness zone 4.

Observations

Very easy to see around the top stations of ski lifts in Austria, Bulgaria and elsewhere in central and SE Europe; it is usually abundant and covers large areas at and above the treeline.

Remarks

The epithet is an Italian vernacular name for this pine.

The low shrubby growth with a bowed basal section of stem is an adaptation to deep snow cover and avalanches; the erect branch ends are flattened down by the weight of snow, to spring erect again during the spring thaw; see Berkutenko (1993) for a discussion of this phenomenon with regard to the similar growth structure of Pinus pumila. The Bulgarian name Klek ('knee') refers to the growth form.

Very rarely plants with cone characters of subsp. mugo make small trees with a straight stem, but only where sympatric with either subsp. uncinata or hybrids with it, suggesting tree form is due to hybrid influence (Christensen 1987).

Citations

Berkutenko, A. 1993. The remarkable Pinus pumila. Int. Dendrol. Soc. Yearbook 1992: 41-46.

Bigler, Christof and A. Rigling. 2013. Precision and accuracy of tree-ring-based death dates of mountain pines in the Swiss National Park. Trees - Structure and Function. http://dx.doi.org/10.1007/s00468-013-0917-6.

Businský, R. 1998. Pinus mugo agg. in former Czechoslovakia - taxonomy, distribution, hybrid populations and endangering. Zprávy Ces. Bot. Spolec. Praha 33: 29-52. [in Czech; brief English summary].

Christensen, K.I. 1987. Taxonomic revision of the Pinus mugo complex and P. × rhaetica (P. mugo × sylvestris) (Pinaceae). Nordic J. Botany 7: 383-408.

Jovanovic, Branislav. 1986. "Pinus mugo" in Flora Srbije. Belgrade: Serbian Academy of Sciences and Arts.

Turra, A. 1765. Dei vegetabili di Monte Baldo. Giorn. Italia Sci. Nat. 1:152.

See also

Elwes and Henry 1906-1913 at the Biodiversity Heritage Library (P. mugo treated as P. montana). This series of volumes, privately printed, provides some of the most engaging descriptions of conifers ever published. Although they only treat species cultivated in the U.K. and Ireland, and the taxonomy is a bit dated, still these accounts are thorough, treating such topics as species description, range, varieties, exceptionally old or tall specimens, remarkable trees, and cultivation. Despite being over a century old, they are generally accurate, and are illustrated with some remarkable photographs and lithographs.