|Photo by Patricia Howell, Atlas of Florida Vascular Plants|
|Division:||Magnoliophyta - Flowering plants|
|Class:||Magnoliopsida – Dicotyledons|
| Macroptilium atropurpureum|
(Lam.) K. Koch
|Natural range of Macroptilium atropurpureum from USDA NRCS Plants Database.|
Common name: Purple bushbean
Synonym: Phaseolus atropurpureus Moc. & Sessé ex DC. USDA NRCS Plants Database
A perennial species in tropical regions and an annual in subtropical climates. It is a trailing, climbing, twining species with a deep, swollen taproot. 
It is a native to tropical continental America, and is distributed through out the tropics.
Habitats include disturbed ruderal areas such as lawns, along railroad beds, and pastures.  It has great economic importance in cover crop, forage and prevents soil erosion.  A long, deep taproot and the ability to reduce evapotranspiration by shedding its leaves allows for tolerance of dry conditions.
M. atropurpureum can be nodulated by a range of alpha-rhizobial strains, which allow for nitrogen-fixation and allows the plants to thrive in nutrient poor soils. Soil, pH, phosphate, and CaCO3 content and granulation influence the type of rhizobial nodulation that occurs. When M. atropurpureum grows under dry, high temperature conditions, Burkholderia tuberum induces nitrogen fixing nodules. 
Flowers and fruits August through October.  It has been observed that flowering is initiated in response to the onset of dry periods and shorter days while vegetative growth resumes with the return of moist conditions.
In subtropical climates, it displays an annual lifecycle, while in tropical climate is perennial. Perennation of this species has been observed to be associated with survival of the original crowns that develop from seedlings. Individuals that are produced by vegetative reproduction from rooted stolons, are short lived and only survive until the end of the wet season. 
Seed bank and germination
Seed reserves are important for individual replacement in subtropical conditions where the species displays an annual lifecycle. 
Post-fire, plants recover well from crowns or stems if perennial and soil seed reserves if annual.
The following Hymenoptera families and species were observed visiting flowers of Macroptilium atropurpureum at Archbold Biological Station: 
Apidae: Apis mellifera
Megachilidae: Megachile georgica
Diseases and parasites
This species is susceptible to a variety of diseases and viruses. Under conditions of high rainfall and high humidity, Rhizoctonia solani causes foliar blight that can reduce leaf yields by 80%; however, plants can recover with a return to dry conditions. Synchytrium phaseoli, false rust, occurs during periods of high humidity. Viruses include mung bean yellow mosaic virus and passionfruit woodiness potyvirus.
Conservation and management
Cultivation and restoration
M. atropurpureum is of economic importance for forage, cover crop and preventing soil erosion.  It has been observed to thrive in light stocking and/or rotational grazing. Regular heavy grazing causes loss of buds, shorter plant growth, reduced seed set, and declining soil seed reserves.
Flowers of Macroptilium atropurpureum
Photo by Patricia Howell, Atlas of Florida Vascular Plants
References and notesCalles, T., G. P. Lewis, et al. (2015). "Lectotypification of Macroptilium atropurpureum (Leguminosae)." Kew Bulletin 70(1).
- Morris, J. B. (2010). "Morphological, pheological and reproductive trait analysis for the pasture species, siratro (Macroptilium atropurpureum)." Tropical Grasslands 44: 266-273.
- [] Encyclopedia of Life Accessed: February 10, 2016
- Florida State University Robert K. Godfrey Herbarium database. URL: http://herbarium.bio.fsu.edu. Last accessed: February 2016. Collectors: Loran C. Anderson. States and Counties: Florida: Clay, Escambia, Leon, Nassau, Osceola, Putname. Countries: Honduras. Compiled by Tall Timbers Research Station and Land Conservancy.
- Cook, B.G., Pengelly, B.C., Brown, S.D., Donnelly, J.L., EAgles, D.A., Franco, M.A. Hanosn, J., Mullen, B.F., Partridge, I.J. Peters, M., Shultze-Kraft, R. (2005). "Tropical forages: An interactive selection tool." CD-ROM. CSIRO, DPI&F (Queensland), CIAT and ILRI.
- [] Feedipedia Accessed: February 10, 2016
- Angus, A. A., A. Lee, et al. (2013). "Nodulation and effective nitrogen fixation of Macroptilium atropurpureum (siratro) by Burkholderia tuberum, a nodulating and plant growth promoting beta-proteobacterium, are influenced by environmental factors." Plant and Soil 369(1): 543-562.
- [] Tropical Forages Accessed: February 10, 2016
- Gutteridge, R. C. (1985). "Survival and Regeneration of Four Legumes Oversown into Native Grasslands in Northeast Thailand." Journal of Applied Ecology 22(3): 885-894.
- Deyrup, M.A. and N.D. 2015. Database of observations of Hymenoptera visitations to flowers of plants on Archbold Biological Station, Florida, USA.