Memecylon

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Memecylon is a plant group in Melastomataceae. It consists of 350-400 species of small to medium-sized trees and shrubs occurring in the Old World tropics.[1][2][3] Memecylon is a monophyletic group basal to the Melastomataceae clade.[4] Memecylon taxa have more than 600 published basionyms.[1][4] Diversity of this group is concentrated in tropical Africa, Madagascar, Sri Lanka, India and Malaysia.[5]

Etymology

The name Memecylon is derived from 'memaecylon' as used by ancient Greek philosophers Dioscorides and Pliny to describe the red fruits of Arbutus unedo (oriental strawberry tree), an unrelated plant group, alluding to the pink to reddish berries often produced by Memecylon.[4] Some vernacular names in different regions of the world are given below. English: "Blue mist plant", Hindi: Anjan; Malayalam: Aattukanala [ആറ്റുകനല], Kaasaavu: [കാശാവ്], Kaayaampoo: [കായാമ്പൂ]; Odia: Neymaru; Olle Kudi, Alimar (ಒಳ್ಳೆ ಕುಡಿ, ಅಳಿಮರ) in Kannada ;Sinhala: Korakaha, Welikaha; Tamil: Kaya.[6]

Morphology

Memecylon sensu lato can be diagnosed by exstipulate leaves, four-merous bisexual flowers, anthers opening by slits, enlarged connectives bearing terpenoid secreting glands and berries.[7] Memecylon sensu stricto can be distinguished from other Memecyloids by obscure nervation on leaves, non-glandular roughened leaf surface having branched sclerids, imbricate calyx, unilocular ovary and large embryo with thick and convoluted cotyledons.[5]

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]

Distribution

This group is distributed in approximately 53 countries of the Old World tropics and occupies a wide range of habitats. Memecylon taxa have been reported from montane forests, tropical lowland forests, grasslands, tropical rainforests with low to high rainfall, rocky mountain regions and regions with low to high temperature and a considerable overlap between ranges of different taxa.[3][5][8] Most of the plants in this group are regionally or locally endemic. Endemic Memecylon are reported from 21 countries.[5][9][8][10][11] The global distribution of this group is shown in the following Figure and some of the countries which have endemic Memecylon species are listed in the table.

File:Map of Memecylon.jpg
Global distribution of Memecylon. Regions in red include presence data of Memecylon. Sources: GBIF geographic occurrence data and locality data in NCBI database

Table1. Number of Memecylon taxa reported from different countries

Country Total Number of Memecylon
Andamans 9
Angola 4
Australia 3
Borneo 18
Cambodia 10
Cameroon 27
Ceram Island 3
Central African Republic 2
China 16
Congo 10
Democratic Republic of Congo 1
Equatorial Guinea 7
Fiji 3
Gabon 24
Ghana 4
Guinea 6
India 39
Indonesia 14
Ivory Coast 6
Java 9
Kenya 6
Laos 7
Liberia 9
Madagascar 138
Malawi 2
Malaysia 29
Mascarene Islands 4
Mauritius 5
Mayotte 1
Mozambique 3
Myanmar 12
New Guinea 14
Nicobar Islands 2
Nigeria 5
Philippines 16
Papua New Guinea 9
Reunion 2
Seychelle 2
Sierra Leone 4
Simalue Island 2
Singapore 12
South Africa 2
Sri Lanka 32
Sumatra 10
Taiwan 2
Tanzania 10
Thailand 21
Tonga 1
Uganda 1
Vanuatu 1
Vietnam 15
Zambia 2
Zimbabwe 1

Phylogeny

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 was based on low-copy nuclear loci using representative taxa across the old world tropics, and this study revealed biogeography and ancestral states of this plant group.[17] In addition, there is a fine-scale study associated with South African Memecylon showing the reticulate evolution of this group.[18]

Pollination and seed dispersal

The dense and axillary showy clusters of Memecylon florets do not produce nectar. These flowers are visited by pollen-gathering bees who vibrate or manipulate the anthers.[7] Anthers open by longitudinal slits and exposed pollen invites pollen gathering bees. Anther appendages serve as a hold for bees’ legs. These flowers have terpenoid secreting glands and bees collect terpenoids. Therefore, buzz pollination is also favored. Berries are dispersed by birds and mammals. Populations of Memecylon are widely scattered within the forests as would be expected in bird-dispersed species.[7]

Ecology

Memecylon produce flowers and fruits more regularly than many trees of the equatorial forests. It provides a food supply for wildlife as a source of fruits. Different sympatric groups appear to segregate mainly by soil moisture.[7]

Ethnobotany

Memecylon has economic, medicinal and horticultural values.[7] A yellow dye and a mordant can be extracted from the leaves. They are traditionally used for dyeing silk in Thailand and the robes of Buddhist monks in Sri Lanka.[6] Fruits are edible and some are used as spices.[7] This group provides hard and valuable timber used for building houses and boats. Wood is used to make rafters, house posts, fuel wood, charcoal, tools, and handles.[19] An infusion of leaves is used as astringent for ophthalmia.[20] The bark is applied as a poultice to bruises.[20] Root and heartwood decoctions are used to bring down fever associated with colds, chicken pox and measles.[4][6]

A list of Memecylon species

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A number of taxa have been recently re-assigned to other species. These include:

Sources

  • Plants of World Online ((POWO): Memecylon L.: Accepted Species.[21]

References

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