Verbena urticifolia is a herbaceous

Herbaceous plant

A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...

 plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 in the vervain family (Verbenaceae

Verbenaceae

Verbenaceae, commonly known as the verbena family or vervain family, is a family of mainly tropical flowering plants. It contains trees, shrubs and herbs notable for heads, spikes, or clusters of small flowers, many of which have an aromatic smell.Recent phylogenetic studies have shown that...

). It belongs to the "true" vervains of genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Verbena

Verbena

Verbena , verbenas or vervains, is a genus in the family Verbenaceae. It contains about 250 species of annual and perennial herbaceous or semi-woody flowering plants. The majority of the species are native to the New World from Canada south to southern Chile, but some are also native in the Old...

.

White Vervain has opposite, simple leaves

Leaf

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 on thin, rigid, green stems. The small flowers are borne in spikes

Raceme

A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...

; they open in summer and unusually for this normally bluish-flowered genus are white.

It might be closest to a group that might include such North American species as V. lasiostachys

Verbena lasiostachys

Verbena lasiostachys is a species of verbena known by the common name western vervain. It is native to western North America from Oregon to Baja California, where it is widespread and occurs in many types of habitat, including disturbed areas, where it grows as a common weed. This perennial herb...

or V. menthifolia

Verbena menthifolia

Verbena menthifolia is a species of verbena known by the common name mint vervain. It is native to the southwestern United States and northern Mexico, where it occurs in many types of open, dry habitat such as desert scrub. This perennial herb produces one or more rough-haired, erect stems up to...

, and the Common Vervain (V. officinalis) from Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. As these, it is diploid with 14 chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

s altogether. The relationship of the Swamp Verbena (V. hastata) to these species is more enigmatic; its evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 might have involved hybridization with the White Vervain or a related species in the past.