A primer on lagerstroemia, All you've ever wanted to know

Botanist Thawatchai Santisuk has written the perfect companion for the many plant lovers who have trouble telling species of this large and lovely genus apart

Trees in the genus Lagerstroemia are a common sight along many of Bangkok's roads, among them Rama IV, Si Ayutthaya, Phetchaburi and Phitsanulok leading to Government House. But although they comprise several species, at first glance they all look so similar that not many people can tell them apart. Adding to the confusion is the fact that the trees are called by different names in different localities, and some people lump them together under one name, generally tabaek, or salao, or inthanin.

PRETTY IN PURPLE: The flowers of ‘inthanin-bok’, or ‘Lagerstroemia macrocarpa’.

Actually the various species can be differentiated from one another through their trunks, according to botanist Thawatchai Santisuk of the Royal Forest Department, who is an expert on the Lythraceae family of plants that includes Lagerstroemia. In the book, Economic Trees of Thailand, Part One, published in Thai by the department, he writes that if the trunk's surface is grey or whitish grey, smooth and shiny but marked by round, shallow scars, then the tree is tabaek-na (Lagerstroemia floribunda).

However, if the bark is dark brown or dark grey with longitudinal fissures, then it is salao plueak na (Lagerstroemia villosa) or salao bai yao (Lagerstroemia loudonii).

Meanwhile, if the trunk's surface is rather smooth with light brown bark peeling in thin, small flakes, then it is inthanin-bok (Lagerstroemia macrocarpa) or inthanin-nam (Lagerstroemia speciosa, also called Lagerstroemia flos-reginae).

Lagerstroemia as a genus is composed mostly of trees, although there are also shrubs, such as Lagerstroemia indica, known in Thai as yikeng, which is native to China. The trees mostly have opposite leaf patterns but there are also some species with alternate leaves, with clearly visible buds on the leaf axil. Inflorescence comes in different sizes at the tip of branches. According to Mr Thawatchai, Thailand has 14 native species, all of which are on the protected species list.

Most Thais know three common species _ tabaek or tabaek-na, salao and inthanin _ although not many know which one is which. In the book, Mr Thawatchai writes that apart from their trunks, there are other characteristics that differentiate the different species from one another. I have taken the liberty to reproduce his descriptions here, to help us identify the trees.

Tabaek-na (Lagerstroemia floribunda) is a big tree 15 to 30 metres high, with a high buttress and a round-shaped crown. Young leaves are reddish and covered with soft, short hairs that disappear as the leaves mature. The edges of mature leaves roll upwards. The flower buds are shaped like tops, with short knots that look like nipples at the tip. When fully open the flowers are 3-4cm wide. The petals are purple or pinkish purple, then fade to nearly white before they fall. A semi-deciduous tree, tabaek-na sheds its old leaves in May and June, but before all could fall, new leaves develop. Flowering time is July to September, depending on locality and environmental factors. Old fruits crack open and release their seeds the following March.

Salao bai yai (Lagerstroemia loudonii) is a medium-sized tree 10-20m high, with round, dense canopy and dark green leaves. Its fissured bark is thick, and as its name implies, it has big leaves, 16-24cm long with parallel margins and soft, yellowish hairs on both sides of both young and mature leaves, which have pointed tips. Bright purple flowers come in big clusters that are cylindrical in shape. Flowers when fully open are 7-8cm wide. Both the peduncle, or the stem of the cluster of flowers, and the pedicel, or the stem of the individual flowers, are covered with soft, yellowish hairs. Leaves begin to fall in February, and flowering period is March and April. Fruits are almost round and mature in November; they crack open and release their seeds from November to February. Salao bai yai is found in mixed deciduous and dry evergreen forests in all regions of Thailand except the south.

Inthanin bok (Lagerstroemia macrocarpa) is a medium-sized tree eight to 20 metres tall. It has a round canopy with long, willowy stems sweeping down to cover more than half of the tree's main trunk, which is usually spotted with scars. Big leathery leaves are 12-17cm wide and 20-30cm long, dark green and shiny without any hair whether young or old. Individual flowers are big, 10-12cm wide, with cup-shaped sepal covered by soft thin hair. Petals are bright purple, which fade to nearly white before they fall. Leaves begin to fall in February, and new leaves develop at the same time with flowers from March to May. Fruits are small and mature in November and December, with seeds released in January. It is native to dry dipterocarp forests in the north and in mixed deciduous forests throughout Thailand except the southern region.

Inthanin-nam (Lagerstoremia speciosa) is a medium-sized to big tree, 10-25m tall, with branches growing from the lower part of the main trunk, which is usually not straight. The canopy has a round shape, and in the wild where trees grow naturally, the willowy stems sweep down to the ground to shroud nearly the whole trunk. The leaves, 11-25cm long, have a slightly pointed tip. Flowers are purple, purple pink and pink, all in the same cluster. Before they fall in February and March, the green leaves change to red, yellow or orange. Flowering time is March to May, and fruits mature in October through December. It is found in mixed deciduous forests throughout Thailand and in moist evergreen forests of the south.

Thanks to Mr Thawatchai's descriptions, I have come to know the trees better, and I hope you have too.

Email nthongtham@gmail.com.

GETTING TO THE BOTTOM OF IT: Various species of ‘Lagerstroemia’ can be identified by their trunks.

About the author

Writer: Normita Thongtham
Position: Writer