An introduction to the genus Melastoma L.
Table of Contents
The following texts are extracts of the dissertation "Phylogeny and systematics of the genus Melastoma (Melastomataceae) (German summary) of Karsten Meyer. Literature citations are linked to a list of melastome literature of more than 900 citations and more than 180 kb!
1. History of the genus Melastoma
The first valid description of a Melastoma-species dates back to Linné (1753) who introduced M. malabathricum, but the name "Melastoma" dates back to Burmann (1737). At first, nearly all Melastomataceae were described as Melastoma. Therefore, the number of species increased to 69 (Desrousseaux 1797).
The present circumscription to Asiatic melastomes follows Naudin (1849) who described Melastoma as hairy shrubs growing in India, China, the Sunda Islands, some islands of Oceania and in Australia. Their ovate or lanceolate leaves have entire margins and 3, 5 or 7 nerves. The inflorescences are fascicles or glomerules at the branch tips, the calyces are hairy or scaly, the petals violet.
The last complete revision was conducted by Cogniaux (1891). Many species were described later, especially for Malaysia and the Philippines, but only a partial revision for Indonesia (Bakhuizen van den Brink jr. 1943) was published to date.
2. Systematic position of Melastoma and the tribe Melastomeae
Traditionally, the family Melastomataceae is divided into several tribes (Renner 1993). New molecular data (Clausing & Renner, in prep.) show that not all of these tribes are monophyletic and have to be split. The Melastomeae, on the other hand, are monophyletic. Morphological synapomorphies of the tribe are cochleate seeds and bristly ovaries. A very characteristic feature, the elongated connectives of the stamens (pedoconnectives), are synapomorphies with its sister clade, the Microlicieae.
The Melastomeae are the only pantropically distributed tribe. Their basal taxa are neotropical, the paleotropical taxa originate monophyletically within the neotropical genera. This points, together with the neotropical sister group Microlicieae, to an American origin of the tribe and a subsequent colonization of Africa and Asia.
Melastoma itself is monophyletic and the most derived of the analyzed genera. Its sister groups are the genera Dissotis (Africa) or Osbeckia (Africa, Asia). Osbeckia differs from Melastoma by the combination of dry fruits with isomorphic stamens, and Dissotis by the African distribution.
A phylogeny of the Melastomeae is presented below in the next section "3. Phylogenetic analysis".
3. Phylogenetic analysis
For the phylogenetic analysis of Melastoma and the other Old World genera of the Melastomeae a morphological and a molecular dataset was compiled. The morphological data comprised all paleotropical genera but resulted in a nearly unresolved phylogeny. The molecular data lack several African genera but resolved the relationships within the examined taxa.
The molecular dataset comprised 45 taxa of paleo- and neotropical Melastomeae, Microlicieae, other Melastomataceae and a Myrtales outgroup of 3 taxa. The variable part of the chloroplast gene ndhF was sequenced and aligned. This resulted in a consensus sequence of 1033 characters, 263 (25,5 %) of them are phylogenetically informative. The analysis was done with the program PAUP* 4.0b2 and resulted in 1890 trees of 995 steps. The STRICT CONSENSUS-tree is presented below.
Click to get a larger image (82K).
Basal in the Melastomeae is a clade of Arthrostemma and Rhexia. Both genera share characters like irregularly tuberculate seed testas ( which might be a synapomorphy), 4-merous flowers and glandular hairs. Rhexia was previously only member of tribe Rhexieae, but share cochleate seeds with the Melastomeae.
The position of the genus Centradenia was unclear. It was placed in Bertolonieae, Microlicieae, and Melastomeae because of seed and stamen characters. Molecular data now place Centradenia within the Melastomeae.
Dissotis appears to be monophyletic, but only three species of this large genus were included in the analysis. It is possible that more detailed analyses show Dissotis as para- or polyphyletic genus.
Osbeckia appears to be polyphyletic, and recent studies on African Melastomeae (Jacques-Fèlix 1994) split this mainly Asian genus.
4. Distribution of Melastoma
The genus is centered in Southeast Asia, where the largest number of species occur. The whole distribution area ranges in West-East -direction from the isles of the Indian Ocean and India over Indochina to South China and most Pacific islands. In the North Melastoma ranges from the margin of the Himalayas over Southeast Asia to Northern Australia and Melanesia.
Distribution map made with Online Map Creation.
5. Genus description
Erect or procumbent shrubs or small trees up to 6 m high. Leaves lanceolate to ovate, the base acute, rounded or cordate, the apex typically acute or acuminate, the lamina almost glabrous, strigose or subvillous to villous, the margin entire, 3-, 5- 7- or 9-nerved (the marginal nerves often inconspicuous), the secondary nerves parallel to each other; petiolate. Inflorescences terminal or in distal leaf axils, cymose, rarely flowers solitary or in panicles. Flowers normally 5-merous (often varying in one individual from 5- to 8-merous), diplostemonous, the bracts ovate, sometimes large and conspicuous, deciduous or persistent. Hypanthium campanulate, moderately to densely covered with scales, bristles or complex emergences; sepals triangular to lanceolate, ciliate along the margin, deciduous. Petals obovate, ciliate at least along the apical margin. Stamens dimorphic, connective of the episepalous stamens longer than of the epipetalous stamens and ventrally curved; or stamens isomorphic, connective of all stamens slightly prolonged below the anthers; anthers opening by a single pore, often beaked, connectives with a ventral, bilobed appendage or with 2 ventral appendages, those of smaller stamens (if stamens unequal) curved upwards. Ovary adnate to the hypanthium by 10 septs for about half its length, 5-locular and apically bristly. Fruit a campanulate dry capsule, opening apically, or a fleshy capsule, splitting irregularly transversally or longitudinally, or an indehiscent berry. Seeds minute (< 1 mm), cochleate, and embedded in the pulp.
Chromosome numbers are known for few species only and range from x=8, 10, 12 to x=28 (Xiong 1991, Almeda 1997). Possible base numbers for Melastoma might be x=9 to x=12 (Almeda 1997), dysploidy and polyploidy are known from several genera of Melastomeae, including Melastoma (Almeda 1997). Problems arise from the very small size of melastome chromosomes - which makes them difficult to count - and the large number of synonyms that hampers the assignation of older chromosome counts to presently accepted species.
Secondary plant compounds include mainly tannins and ellagitannins (Hegnauer 1990, Yoshida et al. 1992a, 1992b, 1994). They are hydrolysable di- and trimers and have bactericidal or antiviral (Sakagami et al. 1991) activity. For these reasons chewed leaves or incoctions of roots are used occasionally by indigenic tribes for medicinal purposes (cuts, internal bleedings, gastritis; remarks on several collections). Other uses of Melastoma include wood for burning or fruits for dyeing. Its name comes from the fleshy placentas of most species that are dark blue to black and stain the mouth when eaten (melas: black, greek, stomos: mouth, greek).
6. Identification key
1a. Hypanthium with penicillate or stellate emergences (if simple hairs, then mature fruit a soft berry) 2.
b. Hypanthium with simple scales, bristles, or hairs 9.
2a. Hypanthium with stellate emergences 3.
b. Hypanthium with penicillate emergences (if simple hairs, then mature fruit a soft berry) 4.
3a. Leaves strigose; Borneo 1. M. beccarianum
b. Leaves and entire plant lanuginose; Indochina and Thailand 17. M. saigonense
4a. Mature fruit a dehiscing fleshy capsule, campanulate; leaves and stems pilose; Philippines 21. M. toppingii
b. Mature fruit an indehiscing blue berry, globose; leaves and stems strigose or glabrous 5.
5a. Creeping shrub, often rooting at the nodes 5. M. dodecandrum
b. Erect shrub, not rooting at the nodes 6.
6a. Connectives of stamens elongated 13. M. orientale
b. Connectives of stamens not elongated 7.
7a. Bracts enclosing the hypanthium for c. 1/2 its length 10. M. montanum
b. Bracts not enclosing the hypanthium 8.
8a. Inflorescence a loose cyme with branches >= 1 cm long; leaves sparsely strigose to glabrous 9. M. moluccanum
b. Inflorescence a dense cyme with branches < 1 cm lon; leaves densely strigose 4. M. cyanoides
9a. Fruit an apically dehiscing dry capsule; inflorescence a many-flowered loose cyme with branches >= 1 cm long 14. M. pellegrinianum
b. Fruit a longitudinally or transversally dehiscing fleshy capsule; inflorescence a few-flowered cyme, or flowers solitary 10.
10a. Hypanthium scales or bristles not imbricate (surface of hypanthium visible) 11.
b. Hypanthium scales or bristles imbricate (surface of hypanthium invisible) 12.
11a. Hypanthium covered with spreading bristles; leaves <= 3 cm long; Bonin Islands 20. M. tetramerum
b. Hypanthium covered with spreading or appressed scales; leaves usually > 5 cm long 18. M. sanguineum
12a. Hypanthium covered with widely spreading scales or bristles 13.
b. Hypanthium with appressed scales 18.
13a. Leaves beneath tomentose 14.
b. Leaves beneath strigose or pilose, but not tomentose 15.
14a. Leave lamina bullate; anthers obtuse; Philippines 2. M. bensonii
b. Leave lamina not bullate; anthers beaked 8. M. minahassae
15a. Branches, petioles, and hypanthium covered with long spreading bristles 16.
b. Hypanthium covered with spreading scales; branches and petiole covered with short, appressed or spreading scales 17.
16a. Bases of bristles on lower leaf surface unbranched; leaves elliptic to lanceolate, strigose to nearly glabrous 18. M. sanguineum
b. Bases of bristles on lower leaf surface branched; leaves elliptic to ovate, pilose 3. M. crinitum
17a. Branches with appressed scales; hypanthium scales long, golden 16. M. sabahense
b. Branches with spreading bristles and scales; hypanthium scales short, brown 22. M. velutinosum
18a. Leaf surface bullate 20. M. setigerum
b. Leaf surface not bullate 19.
19a. Upper leaf surface with few long and many very short bristles; Peninsula Malaysia 15. M. perakense
b. Upper leaf surface with only one type of bristles (if more than one type then not Peninsula Malaysia) 20.
20a. Flowers enclosed in large, pilose bracts > 1 cm long 21.
b. Bracts not enclosing the flowers (if enclosing the flower, then bracts glabrous or strigose) 22.
21a. Leaves lanceolate, olive-brown; hypanthium bristles brownish; Peninsula Malaysia and Borneo 11. M. muticum
b. Leaves ovate, green-olive; hypanthium bristles golden; Indochina 19. M. septemnervium
22a. Inflorescences on old wood, overtopped by subterminal shoots 6. M. imbricatum
b. Inflorescences on young shoots 7. M. malabathricum
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