Botany
Weed of the Month
May, 2010: Rhodomyrtus tomentosa, the downy myrtle (or downy rose-myrtle)
An ornamental shrub that has become naturalized and now forms pure stands in parts of central Florida.
Rhodomyrtus tomentosa, the downy myrtle (or downy rose-myrtle)
Photograph courtesy of USF Herbarium Slide Collection
Distinguishing Characteristics: This is a well-branched shrub growing to 6 feet tall. The glossy, leathery evergreen leaves have 3 conspicuous main veins, and they are usually densely hairy on the underside with gray or tawny hairs; occasional plants have leaves which are nearly glabrous. The leaves are oval in shape, blunt at the apex, and 2 – 3 inches long. The flowers are about an inch across, and they are borne singly or a few together in the axils of the leaves; they have 5 rose pink petals and a central mass of numerous pink stamens. The juicy berry is about a half-inch across, and it turns dark purple when ripe; it strongly resembles a blueberry in shape.
Rhodomyrtus tomentosa, the downy myrtle (or downy rose-myrtle)
Photograph courtesy of Roger Hammer, Atlas of Florida Vascular Plants
Distribution: The downy myrtle is native to southern and southeastern Asia, from India to the Philippines and Indonesia, where it grows in a variety of habitats from sea level to 7000 feet elevation. It has been introduced into the Pacific islands where it has become seriously invasive. In the United States, it has only been recorded from Florida and Hawaii.
Occurrence in Florida: This species has invaded a variety of plant communities, including scrub, coastal strands and flatwoods in 14 counties, from Pasco and Orange in the north to Collier and Palm Beach in the south.
Similar Species in Florida: Another species in the Myrtaceae, the pineapple guava (Acca sellowiana) has similar flowers and foliage. However, the leaves of this commonly cultivated plant are whitish beneath, at least when young, and they are not 3-nerved. Its flowers have 4 fleshy, edible petals that are cupped and somewhat reflexed, accentuating the central mass of stiff, dark red stamens. A native plant in the Melastome Family, Tetrazygia bicolor, the Florida clover ash, has opposite, 3-nerved leaves that are tomentose beneath, but its flowers are white and are borne in terminal panicles.
Rhodomyrtus tomentosa, the downy myrtle (or downy rose-myrtle)
Photo courtesy of Dennis Girard, Atlas of Florida Vascular Plants
Means of Dispersal: The fleshy berries are eaten by various fruit-eating species of birds and mammals, which then disperse the seeds widely. Each fruit contains as many as 200 small seeds, and these germinate readily. Evidently the plants do not spread by suckers or other vegetative means.
Comments: This is an attractive ornamental, and the fleshy fruits are sweet and edible and can be made into jams and pies. It was introduced into Florida in the 1920’s, and it soon escaped and rapidly became a serious pest. It is fire-resistant, resprouting rapidly after being burned, and it forms dense, pure stands in pinelands and other habitats, mostly in the central part of the state. It is included on Florida’s noxious weed list, and it is also listed as a Category I invasive by the FLEPPC. According to some workers, it has the potential to become as serious an invasive in Florida as Brazilian pepper (Schinus terebinthifolius).
Further Information: Langeland, K.L., H.M. Cherry, C.M. McCormick and K.A. Craddock Burks. 2008. Nonnative plants in Florida’s natural areas. IFAS Communication Services, University of Florida, Gainesville. 193 pp.; http://en.wikipedia.org/wiki/Rhodomyrtus_tomentosa (Accessed: May 3, 2010).
Dr. Richard Weaver, Botanist
Florida Department of Agriculture and Consumer Services
Division of Plant Industry
1911 SW 34 Street
Gainesville, FL 32614
