Memecylon

Stems

Species of larger stature have a characteristic brown bark with narrow and sharp furrows, most are small single stemmed trees. However, the bark of many species of smaller stature is varied and may be papery white or smooth dark red black.^[3][7]

Leaves

Leaves are opposite, short-stalked, elliptic or ovate, mostly with widely spaced pinnate nerves either visible or obscure. Leaves along the twig are all the same size, shiny, glabrous, with entire margins, the node has a characteristic scar between the leaves, the twig bark is typically red, striated and flaky.^[3]

Flowers

The inflorescence is typically dense and axillary. The florets are small (usually less than 5 mm) compared to the other taxa in Melastomataceae, with short fleshy corolla parts. Cymes are bracteate, usually thyrsoid to umbel shaped, often condensed to sessile fascicles of flowers or a few-flowered heads at tips of peduncles. The florets are white or violet, the stamens blue or violet, usually obvious in aggregates, from axillary clusters. Flowers are bisexual, have inferior ovaries, but the parts are otherwise free. The calyx is valvate and there are twice as many stamens as petals.^[3][7]

Fruits

The fruit is from an inferior ovary, typically axillary. The calyx remnants are persistent, and are sometimes blue-black. Fruits are globose or occasionally ellipsoid, pulpy or juicy with one large seed.^[3][7]

Phylogeny based on morphological treatments

The classification of Memecylon has switched back and forth among families Melastomataceae, Myrtaceae and Memecylaceae based on morphological, anatomical and molecular evidence. Early classifications excluded Memecylon and Mouriri from the Melastomataceae mainly based on placentation and seed characters. Subsequent treatments preferred to treat Memecylon as a member of Myrtaceae.^[3] Again, this group has been included in Melastomataceae by Cronquist . After that, morphological and anatomical character analysis of the Melastomataceae and their traditional allies by Renner^[12] identified two major lineages (Melastomataceae and Memecylaceae), and in that classification, Memecylon was placed in the Memecylaceae. Synapomorphies used in this phylogenetic analysis were anther connective and dehiscence, dorsal glands on stamen connectives, endothecium, placentation, locules, seeds, leaf venation, terminal leaf sclereids, paracytic stomata, stomata shape, leaf sclereids, indumentum, ant and mite domatia, wood and growth form characters, which excluded Memecylaceae from Melastomataceae. However, in Memecylon some characters such as seasonal flowering and small size of flowers contributed to the difficulty of assessing relationships based on the morphology. Later, several groups have been either included in broadly defined Memecylaceae or segregated from it. As a result, Memecylaceae comprised the groups Memecylon, Lijndenia, Mouriri, and Votomita^[13].

Phylogeny based on molecular treatments

Molecular phylogenetic analyses using rbcL sequence data showed that the Melastomataceae lineage consists of a subclade formed by Oliniaceae, Penaeaeae, Phynchocalycaceae and Alzateaceae sister to a subclade formed by Memecylaceae and Melastomataceae sensu stricto. Parsimony analysis showed distinct Myrtaceae and Melastomataceae clades.^[14] Subsequently, Bayesian analyses using chloroplast DNA sequences from the rbcL and ndhF genes,^[14] and parsimony and maximum likelihood analyses on rRNA, rbcL and atpB sequences, have shown that Memecylaceae is a sister group to Melastomataceae.^[14] Later studies using combined exon and intron sequences of the nuclear glyceraldehyde 3-phosphate dehydrogenase gene (GapC) has supported the monophyly of Memecylon.^[15] However, the APG IV (Angiosperm Phylogeny Group IV) system of classification, a system of revised and updated classification of flowering plants, now recognizes the groups of Memecylaceae within a broader circumscription of Melastomataceae.^[16]

The most recent phylogenetic analysis of Memecylon included mostly African taxa and was based on two nuclear ribosomal regions, ETS and ITS. Memecylon species discovery in Madagascar increased, and comprehensive taxonomic revisions brought the total number up to 138 species, making Memecylon one of the most species-rich groups in the woody flora of Madagascar. In addition to this high species richness, a high degree of endemism of Memecylon indicated the importance of considering ecogeographic factors when making species identifications in this group.^[8] Therefore, in the latest molecular phylogeny, a combined study of ecogeographic factors has been taken into account.^[8]