Urtica dioica

Grosse-Veldmann, Bernadette & Weigend, Maximilian, 2016, Weeding the nettles IV: A redefinition of Urtica incisa and allies in New Zealand and Australia, including the segregation of two new species Urtica sykesii and U. perconfusa, Phytotaxa 245 (4), pp. 251-261 : 258-259

4. Urtica dioica L. (1753: 984)

Lectotype (designated by Woodland 1982: 283):—herb. Linnaeus 1111.8 (LINN!, photographs in AUB, DAO, M, MTMG).

Synonyms are listed in Grosse-Veldmann & Weigend (2015).

Erect, perennial, rhizomatous herb 0.6–1.5(–2) m, unbranched, but forms branches late in the season. Stem indumentum of many stinging hairs with pluricellular base c. (0.1–) 0.3–0.5 mm overall and erect setae 0.2–0.5 mm long, short stiff bristles and numerous simple trichomes 0.1–0.5 mm long. Leaf lamina 60–120(–150) × 45–85(–100) mm broadly ovate; surface densely pubescent with short simple trichomes 0.1–0.5 mm long and many stinging hairs, adaxially with punctiform cystoliths; leaf base cordate; margins coarsely and regularly serrate, with 14–25 teeth on each side, teeth usually undivided, sometimes with two or three teeth; leaf apex acute to acuminate; stipules free (4 per node) (2–) 5–10 mm long; petioles 20–50 mm long. Plants mostly dioecious, sometimes monoecious. Staminate flowers with tepals c. 0.5 mm long. Pistillate flowers with short tepals 0.2 mm long and long tepals 0.3 mm long, sparsely pubescent, esetulose. Inflorescence (20–) 30–50 mm long and strongly branched. Mature fruit with longer tepals c. 1.3–1.5 mm long, achenes ovoid with a narrowed base and apex, widest below the middle, c. 1–1.5 × 0.6–0.8 mm.

Notes: The weedy form of Urtica dioica L. ( subsp. dioica ) which is found in New Zealand is of unbranched shoots, broad ovate leaves with a cordate base, a dense cover of stinging hairs interspersed with short stiff bristles and simple trichomes and mostly one sex on each individual plant. Like all of the widespread forms of Urtica , U. dioica is also variable in appearance. A very broadly-leaved form which is morphologically similar to the weedy form, but which has only few stinging hairs and a dense and soft pubescence occurs in dry forests in eastern Germany and Poland. The weedy form is absent from undisturbed, humid and nutrient rich forests (e.g. in Europe, in the Southern Alps and on the Balkan pensinsula) where it is replaced by narrow-leaved “forest forms” of U. dioica with only few stinging hairs and a more or less dense pubescence. Robust and low-growing plants with a very dense cover of stinging hairs, deeply serrate leaf margins and strongly branched and dense inflorescences are typically found in alpine pastures on calcareous ground e.g. in the Southern Alps and the Pyrenees. Plants with high moisture demands are restricted to river banks in central and eastern Europe and are characterized by a stiff, erect and very robust habit, narrow leaves, few stinging hairs and a sparse pubescence (see Weigend 2005, Grosse-Veldmann & Weigend 2015).

In overall appearance, typical U. dioica is very similar to native U. incisa , but molecular data clearly show it to be only remotely related. Morphologically it can be differentiated from U. incisa by its broader leaf shape, a dense cover of stinging hairs, strongly branched inflorescences and ovoid achenes.

Distribution:— Urtica dioica L. occurs throughout Eurasia and China and has been introduced to eastern USA and Canada, as well as to Chile and New Zealand. In New Zealand it is known from both the North and South Islands. It has not (yet) been reported from Australia.

Habitat and ecology:— The common lowland and coastal, weedy form occurs in nutrient rich open habitats, on road sides, waste grounds and disturbed sites at low and intermediate elevations. In New Zealand it is found on river terraces, open meadows, roadsides, disturbed sites, on pasture and on beaches in a variety of substrates.

Phenology:— Urtica dioica L. flowers throughout the year.

Conservation status:— According to the New Zealand Threat Classification System ( de Lange et al. 2013), Urtica dioica L. is considered “Exotic”.

Additional specimens examined:— NEW ZEALAND. Greater Wellington (North Island): Wellington Ecological Distr. , Somes (Matiu) Island , S 41° 15.5’, E 174° 52.0’, 20 m, 19 Sept. 1991, P.J. de Lange 1050 ( CHR 474966 !) ; Manawatu-Wanganui (North Island): Wanganui Distr., Wanganui city, Papaiti , Whanganui River , S 39° 51’, E 175° 5’, 20 m, 7 Nov. 1993, C. C. Ogle 2654 ( CHR 495175 !) ; Wellington Land Distr., Wanganui Distr., Fordell, No. 2 Line , “Aird” farm, S 39° 57 ‘, E 175° 11’, 160 m, 2 Nov. 1997, C. C. Ogle 3298 ( CHR 515018 !) .

Specimens from cultivation:— Original collection: NEW ZEALAND. Canterbury ( South Island ): Canterbury Land Distr. , Hope , north of Lewis Pass , 13 Jan. 2004, collector unknown, cultivated in: Canterbury ( South Island ): Canterbury Land Distr., Christchurch, St. Albans, 115 Packe Str., 13 Jan. 2004, W. R. Sykes 18/04 ( CHR 605119 !) ; Hawke’s Bay ( North Island ): Hawke’s Bay Land Distr. , Weleda ( NZ) Limited Gardens, Havelock North, 29 Nov. 2011, QA Technician s.n. ( CHR 554345 A!, CHR 554345B!) .