**Urtica urens L. (Urticaceae)**

**Dwarf Nettle**

**Description**. Monoecious annuals; stems 15-50 cm tall, erect, simple
or branched from the base, bristly with stinging hairs. Leaves opposite,
stipulate (stipules 1-3 mm long, oblong), long-petiolate, upper ones
usually larger than lower, blades 1-4 cm long, elliptic to ovate, nearly
glabrous, margins deeply serrate. Flowers in dense, axillary, oblong
clusters; calyx ca. 2-3 mm long, the staminate sepals equal, partly
fused, the pistillate ones unequal, ± free, with ciliate margins;
corolla absent; stamens 4 ; ovary superior, with one style. Fruit an
achene, 1.5-2.5 mm long, triangular. In California, flowering from
February to July. (Clapham et al. 1962, Abrams 1944, Fernald 1950,
Gleason and Cronquist 1991, Woodland 1993, Munz 1959).

**Note**: Dwarf nettle can be confused with the native, relatively rare
*Hesperocnide tenella* Torrey, which has the pistillate sepals equal in
size and almost completely fused. Both species often occur in the same
or similar habitats.

**Geographical distribution**. A native of Europe, dwarf nettle has
become naturalized throughout western and eastern North America, Chile,
Australia, New Zealand, southern Africa, and Hawaii. (Arnold and de Wet
1993, Chapman 1991, Fernald 1950, Gleason and Cronquist 1991, Montenegro
et al. 1991, Webb et al. 1988, Wagner et al. 1990).

*Urtica urens* was first reported from California in the mid 19th
century and had become widespread by the end of the 19th century (Parish
1920, Robbins 1940). It has been reported from San Miguel, Santa Rosa,
and Santa Cruz islands (Junak et al. 1997) and is widely distributed in
California west of the Sierra Nevada (Anonymous 1998, Woodland 1993).

**Reproductive and vegetative biology**: Most species of *Urtica* are
pollinated by wind (Faegri and van der Pijl 1966, Proctor et al. 1996).
*Urtica urens* is self-compatible, and capable of self-pollination; seed
set, relative to the perennial *U. dioica*, is high, even when plants
are depauperate (Boot et al. 1986). Seed dormancy is extended if seeds
are buried; long days appear to be a primary factor for germination
(Milberg and Andersson 1997).

**Ecological distribution**. Dwarf nettle occurs on disturbed sites,
gardens, orchards, and in fallow or uncultivated fields (Clapham et al.
1962, Abrams1944, Fernald 1950, Munz 1959, Woodland 1993).

**Weed status.** *Urtica urens* is not considered a noxious weed in
agricultural or horticultural practice, at least at a global level (not
listed by Holm et al. 1977), nor is it considered a noxious weed by the
State Dept. of Food and Agriculture (Anonymous 1996). It is not listed
as a weed in the United States in Lorenzi and Jeffery (1987).

**Microbial pathogens**. No literature was found that reported microbial
pathogens of *Urtica*.

**Insect pathogens**. No literature was found that reported insect
pathogens of dwarf nettle, which may be resistant to general insect
herbivory (Mutikainen and Walls. 1995).

**Herbicide control**. No literature was found that reported herbicide
control of *Urtica*. However, Lorenzi and Jeffrey (1987) listed several
herbicides (dicamba, 2,4-d, atrazine, diuron, and mmteribuzin among
others) useful in controlling *Parietaria*, another genus in the
Urticaceae.

**Literature Cited**

Anonymous. 1996. Exotic pest plants of greatest ecological concern in
California as of August 1996. California Exotic Pest Plant Council. 8
pp.

Anonymous. 1998. California county flora database version 2, Santa
Barbara Botanic Garden and USDA National Plants Data Center, Santa
Barbara and New Orleans. URL = plants.usda.gov

Abrams, L. (ed.) Illustrated flora of the Pacific states. Volume 1.
Ophioglossaceae to Aristolochiaceae. Stanford University Press,
Stanford, California. 538 pp.

Arnold, T. and B. de Wet. 1993. Memoir 62. Plants of southern Africa:
names and distribution. National Botanical Institute, Pretoria. 825 pp.

Boot, R., D. Raynal, and J. Grime. 1986. A comparative study of the
influence of drought stress on flowering in *Urtica dioica* and *Urtica
urens*. Journal of Ecology. 74: 485- 495.

Chapman, A. 1991. Australian plant name index. Q-Z. Australian
Government Publishing Service, Canberra. pp. 2477-3055.

Faegri, K. and L. Van der 1966. The principles of pollination ecology.
Pergamon Press, Oxford. 248 pp.

Fernald, M. 1950. Gray's manual of botany. Eighth Edition. American Book
Company, New York. 1632 pp.

Gleason, H. and A. Cronquist. 1991. Manual of vascular plants of
northeastern United States and adjacent Canda. 2nd. edition. New York
Botanical Garden, Bronx. 910 pp.

Holm, L., D. Plucknett, J. Pancho, and J. Herberger. 1977. The world's
worst weeds: distribution and ecology. University Press of Hawaii,
Honolulu. 609 pp.

Junak, S., S. Chaney, R. Philbrick, and R. Clark. 1997. A checklist of
vascular plants of Channel Islands National Park. Southwest Parks and
Monuments Association, Tucson, AZ. 43 pp.

Lorenzi, H. and L. Jeffery. 1987. Weeds of the United States and their
control. Van Nostrand Company, New York. 355 pp.

Milberg, P. and L. Andersson. 1997. Seasonal variation in dormancy and
light sensitivity in buried seeds of eight annual weed species. Canadian
Journal of Botany. 75: 1998- 2004.

Montenegro, C., S. Teillier, P. Arce, and V. Poblete. 1991. Introduction
of plants into the

mediterranean-type climate area of Chile. pp. 103-114. In Groves, R. and
F. Di Castri.

Biogeography of Mediterranean invasions. Cambridge University Press,
Cambridge. 485 pp.

Munz, P. 1959. A flora of California. University of California Press,
Berkeley. 1681 pp.

Mutikainen, P. and M. Walls. 1995. Growth, reproduction and defence in
nettles: responses to herbivory modified by competition and
fertilization. Oecologia. 104: 487-495.

Parish, S. 1920. The immigrant plants of southern California. Bulletin,
Southern California Academy of Sciences 19: 3-30.

Proctor, M., P. Yeo, and A. Lack. 1996. The natural history of
pollination. Timber Press, Portland, Oregon. 479 pp.

Robbins, W. 1940. Alien plants growing without cultivation in
California. Agricultural Experiment Station. Bulletin 637. University of
California, Berkeley. 128 pp.

Wagner, W., D. Herbst, and S. Sohmer. 1990. Manual of the flowering
plants of Hawaii. 1853 pp.

Webb, C., W. Sykes, and P. Garnock-Jones. 1988. Flora of New Zealand.
Volume 4. Naturalized pteridophytes, gymnosperms, dicotyledons.
Department of Scientific and Industrial Research, Christchurch. 1365 pp.

Woodland, D. 1993. Urticaceae. pp. 1082-1083. In J. Hickman (ed.) The
Jepson Manual: higher vascular plants of California. University of
California Press, Berkeley. 1400 pp.