The Principal Weedy Melastomaceae in Hawaii 
D. L. Plucknett and B. C. Stone 1 
None of the numerous species of Melasto- 
maceae is native to the Hawaiian Islands, yet at 
present at least a dozen species in nine different 
genera are found as weeds or seminaturalized 
plants in various localities in the Islands. Some 
of these species are hardly known out of cul- 
tivation, others are frequent in certain small 
areas, while a few are well-known common 
plants on most of the islands in the chain. Cer- 
tain areas have become thickly populated with 
one or another of these species, and waste and 
pasture areas have been invaded, becoming in 
some cases nearly impenetrable thickets. Two 
or three of these species must be regarded as 
noxious weeds. 
In Hillebrand’s Flora of the Hawaiian Is- 
lands (1888) there is no mention of any melas- 
tomaceous species. Degener (1935: family 274) 
mentions Heterocentron, and (1930: 226) 
mentions Tibouchina semidecandra and Melas- 
toma malab athricum. Earlier, W. T. Pope 
(1929: 147) had mentioned Melastoma decem- 
fidum and stated that it had escaped from cul- 
tivation on Kauai, and had been introduced 
(presumably from a Florida nursery) in 1916. 
It seems from recent collections that this plant 
mentioned by Pope is, as Degener indicated, M. 
malab athricum; although both species are pres- 
ent in the Islands, only this one has been found 
on Kauai. The Tibouchina is said to have been 
introduced to Hawaii in 1910. 
Degener indicated the pestiferous nature of 
these plants, and his prediction that they would 
spread has come true. At present they have a 
very spotty distribution, but where they have 
spread they often form virtually pure stands 
which have blighted many areas of natural veg- 
etation and have become a foe of both the agri- 
culturist and conservationist. Hosaka ( 1945 ) 
referred to Melastoma malabathricum as "an ag- 
1 Department of Agronomy and Soil Science, and 
Department of Botany, University of Hawaii, Hono- 
lulu. Manuscript received June 15, I960. 
gressive shrub that forms dense stands — crowds 
out other plants . . . has no forage value.” 
Recently the extent of bauxitic or aluminous 
soils in Hawaii has been publicized (Sherman, 
1954), and plants which accumulate aluminum 
have been the subject of a paper by Moomaw, 
Nakamura, and Sherman (1959). Among the 
Hawaiian plants found to accumulate aluminum 
was M. malabathricum, a known accumulator 
of aluminum in other areas (Webb, 1954). 
None of the other melastomaceous plants in 
Hawaii was used in the study by Moomaw et al., 
but other species of the Melastomaceae are re- 
ported by Webb to accumulate aluminum. 
The purpose of this paper is to discuss the 
distribution and spread of the noxious Melas- 
tomaceae in Hawaii with special reference to 
the most common species and to provide a key 
and brief descriptions of each as a preliminary 
step for a possible study of bauxitic soils and 
aluminum-accumulating species of Melastoma- 
ceae. 
Three species are found on more than one 
island and may be considered common. These 
are Tibouchina semidecandra, Melastoma de- 
cemfdum, and M. malabathricum. 
Three other species are rather abundant in a 
few isolated locations on one or two islands. 
These are Clidemia hirta, Pterolepis glomerata, 
and Heterocentron subtriplinervium. 
The remaining species are restricted to a few 
small areas and do not threaten to become nox- 
ious weeds. These are Oxyspora paniculata, Ar- 
throstemma latifolium, Tetrazygia bicolor, and 
Medinilla magnifica. Some of these species are 
referred to by Neal (1948: 569). 
KEY TO COMMON SPECIES 
Petals and all anthers brilliant purple; leaves 
densely silvery-pubescent with soft hairs, 
especially on undersides; open shrubs up to 
12-15 ft. tall. ...Tibouchina semidecandra (1) 
Petals pink, stamens pink or yellow; leaves 
301 
