Lagerstroemia includes about 55 species in Australia and eastern Asia as far north as Japan (Qing et al. 2007). They are evergreen or deciduous trees or shrubs with showy flowers and attractive bark. The branchlets are terete or four-angled, rarely with small wings. The leaves are alternate, opposite or in between. The flowers are solitary or in terminal and axillary paniculate cymes; they are hermaphrodite and 6-merous, though 5-merous and 7-merous flowers are common. The calyx is campanulate or funnelshaped with 6–12(–14) veins or ribs; it opens out into narrow or broadly triangular sepals. An additional whorl of sepal-like bracts (epicalyx) may subtend the calyx. The petals are free and alternate with the sepals; they are rounded or oblong with a long, narrow stalk (claw or limb) that inserts into the calyx. The petals are folded in the bud and appear wrinkled when the flower opens; they may be pink, purple or white. The stamens are usually dimorphic, with six solitary stamens with thick filaments and large anthers, surrounding a cluster of 12 to 100 or more stamens with thin filaments and small anthers. The fruit is a hard, dry capsule that splits along three to six longitudinal valves to release numerous one-winged seeds (Furtado & Srisuko 1969, Qing et al. 2007).
The long-cultivated Lagerstroemia indica, the Crape-myrtle, is a classic example of the effect of the differences between the climates of the eastern United States and northern Europe. Even in the warmest sites in southern England it makes a bush that flowers only after the most favourable summers, and is for the most part a waste of space as a garden plant. Where conditions are particularly favourable, as at Killerton in Devon, it can make a trunk and thus display its lovely cream and pinkish red bark. In much of the southern United States, however, and in the Mediterranean, it is among the most magnificent of all small flowering trees, and justly popular. A vast array of cultivars has been selected, some being hybrids with L. fauriei, with characters in combinations of improved flower colours, autumn leaf colouring, bark effects and mildew resistance. Many were created through the work of Dr Donald Egolf and others at the US National Arboretum over several decades (Dirr 1998). The development of the Crape-myrtle is a most important contribution to horticulture, and has made it an exceptionally valuable small tree for gardens in areas with hot summers.
Dirr (1998) gives a summary list of L. indica clones and hybrids, and nursery catalogues and websites will provide others. In addition to the true landscape clones there are numerous seed-raised selections of L. indica in varying degrees of dwarfness, grown as pot or bedding plants for their abundant, rapidly produced flower heads. These have their place, perhaps, but are not a substitute for selected, tree-forming clones.
In addition to the species described below, Lagerstroemia speciosa (L.) Pers. is in cultivation in the warmest areas of the United States. It is a large tropical tree with fine inflorescences of purplish or white flowers, with individual flowers 8 cm across, but is not hardy in our area (Dirr 1998).
All Lagerstroemia will perform best in hot, sunny conditions: it is important to realise that their failure to perform in maritime Europe is not because they are frost tender – they can tolerate temperatures down to at least –20 °C before becoming herbaceous (Dirr 1998) – but is due to the lack of summer heat to encourage vigorous growth and harden the wood. Even in favoured localities it is important to complete pruning by early August to enable new growth to ripen before winter (Dirr 1998). Propagation is by seed or from soft or semi-woody cuttings taken in early summer.
A genus of about fifty species in E. and S.E. Asia and Australia. It was named by Linnaeus after his friend Magnus von Lageström of Gothenburg (1696-1759).