Great variability, especially in degree of indumentum and leaf shape, has led to recognition of many microspecies and infraspecific taxa that are not satisfactorily separated when the species is investigated over its geographic range. Apparent hybridization between Lythrum salicaria and L. virgatum and among the many races of L. salicaria in E Europe and Asia have further confused the taxonomy. Lythrum salicaria is recognized here as a single species with localized variants. Formal names are not recognized for variants within the species until a biosystematic study of the species complex can be made.

Perennial herbs or subshrubs, 0.3-1.5 m tall, scabrous or sparsely to densely gray pubescent [or tomentose], sometimes somewhat glabrescent. Stem erect, 4-angled. Leaves opposite or 3-whorled, sometimes alternate toward stem apex, ovate-lanceolate to broadly lanceolate, 2.5-10 × 0.5-1.5 cm, base rounded, truncate, or semiclasping, apex acute to subobtuse. Inflorescences terminal, spicate, 15-35 cm; bracts broadly lanceolate or deltoid-ovate. Flowers in 1- to multi-flowered whorled axillary cymes, shortly pedicellate. Floral tube 5-8 × 1.5-2 mm, 12-ribbed; sepals deltate, 0.5-1 mm; epicalyx segments erect, linear, 1.5-2 mm, much longer than sepals. Petals reddish purple to rose-purple, lanceolate-oblanceolate, 7-10 × 1.5-3 mm. Fl. Jul-Sep, fr. Oct. 2n = 30, 50, 58, 60.

Perennial, 40-70 cm tall. Leaves ovate-lanceolate, elliptic or lanceolate, acute to acuminate, base cordate-amplexicaul, 6-60 mm long, 2.5-15 mm broad. Spikes 9-45 cm long. Pedicels 1-2 mm. Hypanthium 12-ribbed. Epicalyx longer than or equalling the calyx. Petals 5.5-8.5 mm long, 2-3 mm broad, obovate-spathulate or obovate-oblanceolate. Ovary subsessile, 2-5 mm long, 0.75-1.5 mm broad. Capsule 4 mm long, 1.5 mm broad, narrowed. Seeds obovate, tip ±membranous.

Common in rice fields and wet places, 600-1500 m.

General: Loosestrife Family (Lythraceae). Purple loosestrife is an erect perennial herb that grows up to 2.5 m tall, develops a strong taproot, and may have up to 50 stems arising from its base. Its 50 stems are four-angled and glabrous to pubescent. Its leaves are sessile, opposite or whorled, lanceolate (2-10 cm long and 5-15 mm wide), with rounded to cordate bases. Leaf margins are entire. Leaf surfaces are pubescent.

Each inflorescence is spike-like (1-4 dm long), and each plant may have numerous inflorescences. The calyx and corolla are fused to form a floral tube (also called a hypanthium) that is cylindrical (4-6 mm long), greenish, and 8-12 nerved. Typically the calyx lobes are narrow and thread-like, six in number, and less than half the length of the petals. The showy corolla (up to 2 cm across) is rose-purple and consists of five to seven petals. Twelve stamens are typical for each flower. Individual plants may have flowers of three different types classified according to stylar length as short, medium, and long. The short-styled type has long and medium length stamens, the medium type has long and short stamens, and the long-styled has medium to short stamens. The fruit is a capsule about 2 mm in diameter and 3-4 mm long with many small, ovoid dust-like seeds (< 1 mm long).

Mal et al., 1992, provide a detailed morphological description for L. salicaria. The authors also give details of the tristylous features of this species, as well as an account of its pollen structure and chromosome numbers. The plant’s habit, vegetative, and reproductive structures are illustrated with line drawings.

Other species of Lythrum that grow in the United States have 1-2 flowers in each leaf-like inflorescence bract and eight or fewer stamens compared to L. salicaria, which has more than two flowers per bract and typically twelve stamens per flower. Lythrum virgatum, another species introduced from Europe closely resembles L. salicaria, but differs in being glabrous (lacking plant hairs), and having narrow leaf bases. The latter two species interbreed freely producing fertile offspring, and some taxonomists (Rendall 1989) consider them to be a single species.

Distribution: Purple loosestrife is a hardy perennial herb with stunning spikes of purple flowers. A native of Eurasia, it was introduced to North America in the early 1800's where it first appeared in ballast heaps of eastern harbors (Stuckey 1980). Most likely seeds were transported as contaminants in the ballast or possibly attached to raw wool or sheep imported from Europe (Cole, 1926; Thompson et al., 1987).

The native range of L. salicaria is thought to extend from Great Britain to central Russia from near the 65th parallel to North Africa. It also occurs in Japan, Korea, and the northern Himalayan region. The species has been introduced to Australia, Tasmania, and New Zealand. Since its introduction to North America, this alien plant has spread rapidly into Canada, and throughout most of the United States where it has been reported from all states except Alaska, Florida, Louisiana, and South Carolina. Several factors have contributed to the spread of purple loosestrife such as its potential for rapid growth, its enormous reproductive capacity, lack of natural diseases or predators, its use as an ornamental, and for bee forage (Mal et al. 1992). For current U.S. distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

purple loosestrife, spiked lythrum, salicaire, bouquet violet

The only other species that is similar to Purple Loosestrife is the native Lythrum alatum (Winged Loosestrife), which also occurs in wetlands. This latter species is a smaller and less aggressive plant with winged stems, while the stems of Purple Loosestrife are usually round (sometimes 4-angled). Their flowers are similar in appearance, although Winged Loosestrife has smaller flowers (½" across or less).

This introduced perennial plant is 2-5' tall, branching frequently below the inflorescence. The stems are variably hairy, becoming woody and glabrous below. The leaves are usually opposite, less often whorled in 3's; some of the upper leaves in the inflorescence may be alternate. These leaves are up to 4" long and ¾" across, becoming smaller as they ascend the stems. They are lanceolate, smooth along the margins, slightly hairy (especially the upper leaves), and clasp the stems. The upper stems terminate in long spikes of flowers about ½–2' long. Each flower is about ½–1" across, consisting of 6 purple petals, a green tubular calyx, 6 or more stamens, and a pistil with a stigma that is green and knobby. Each wrinkly petal has a dark purple line toward its base. The hairy calyx has 5 teeth at its apex and several veins along its length. Sometimes the flowers have fewer than 6 petals, and the relative length of their pistils and stamens is variable (in this regard, there are 3 different forms of flowers). The flowers are sessile against the flowering stalks, or they have very short pedicels. The blooming period occurs from mid-summer to early fall, and lasts about 2 months. Each flower is replaced by a small seed capsule that is surrounded by the tubular calyx. This capsule contains many tiny seeds that can float on water or be blown about by the wind. The root system is shallow and fibrous, frequently forming offsets by rhizomes. This plant often forms colonies, and can spread by its seeds, rhizomes, or segments of the roots and stems.