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Genus Acrotrema in Family Dilleniaceae

In botanical taxonomy, a genus (plural genera) is a rank used to group closely related species within a family. In the hierarchy, genus sits below family and above species.

Genera are defined by shared morphological, anatomical, and genetic characteristics (for example, features of flowers, fruits, seeds, or leaves) that indicate a close evolutionary relationship among the species they contain.

Each genus can include one or more species. Examples include Rosa (roses) and Solanum (nightshades, including tomato and eggplant).

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Genus Description

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The genus Acrotrema (Jack) belongs to Myrtaceae (order Myrtales). Jack erected the name in his account of Malayan Myrtaceae (Jack, 1822) to include roughly one to two species from lowland dipterocarp forest of the Malay Peninsula and Borneo. No type species is assigned because the name is now treated as a synonym of Acrotriche (R.Br.) (POWO, 2024; WFO, 2024).

The diagnostic suite of Acrotrema includes a shrubby habit, opposite simple leaves lacking stipules, solitary or paired terminal flowers with five spreading sepals, five free petals, numerous stamens bearing an apical pore (trema), an inferior ovary with axile placentation, and a dry dehiscent capsule. These characters match the Styphelieae clade (Wilson et al., 2005).

Acrotrema is known only from a few early 19th‑century collections from lowland evergreen forest in the Malay Peninsula, with a possible occurrence in northern Borneo, at elevations of 100–500 m. The genus appears to have been endemic to the Malesian rainforest belt, a region with a high Myrtaceae diversity (APG IV, 2016). No modern specimens have been recorded. The few surviving collections are stored in major Asian herbaria and remain a target for re‑examination.

Direct observations of pollination and seed dispersal for Acrotrema are lacking, but flower morphology suggests a generalist insect pollination system. The plants appear to follow the typical Styphelieae life history: a long‑lived woody shrub, leaf turnover in the dry season, and seed germination after fire or disturbance. No chromosome number has been reported for the genus. The shrub’s evergreen foliage is leathery, an adaptation to seasonal drought.

Molecular phylogenetics of the Styphelieae places Acrotrema within the Acrotriche clade (Wilson et al., 2005). Consequently, current world checklists treat the name as a synonym of Acrotriche (R.Br.) (POWO, 2024; WFO, 2024). Earlier taxonomic treatments sometimes recognised Acrotrema as a distinct genus, but the consensus now favour synonymy. The synonymy is supported by shared morphological synapomorphies such as the apical anther pore and capsule type.

Acrotrema has no recorded horticultural, timber, or medicinal uses and is not listed as a weed or invasive species. Its limited distribution and taxonomic obscurity mean it is of no economic significance.

Habitat loss across the Malay Peninsula likely eliminates any remaining Acrotrema individuals, but targeted surveys of historic sites could confirm survival. Integrating the genus into broader Styphelieae conservation planning may help protect its evolutionary legacy.

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