In January 2014, here at the International Moringa Germplasm Collection, we have spider mites.
That brilliant man, Balbir Mathur, of Trees for Life, says "do you avoid planting a tree just because you know that it will be attacked by bugs?" Whether it's a metaphor or a real tree, of course we go ahead! In January 2014, here at the International Moringa Germplasm Collection, we have spider mites. Spider mites are very fond of moringas, especially when they get stressed. Sooner or later, most moringaphiles have to deal with these evil little creatures. Fortunately, as we will see below, treating them is easy.
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Verdcourt's 1985 "A synopsis of the Moringaceae" starts with the sentence The species of Moringa occupy the well-known arid area distribution stretching from southern Angola and southwestern Africa across to Rajasthan with the addition of Madagascar. Verdcourt is referring to a pattern of plant distribution observed across many groups. For example, Commiphora, the myrrh genus, is found in great diversity (many species) and abundance (many individuals) in the dry lowlands of northwestern South Africa and Namibia. As you move north through the tropical deciduous forests of Angola, Commiphora disappears as the West African moist forests come to dominate. They reappear in northeast Africa, especially the northeast Kenya-southeast Ethiopia-Somalia area, where the greatest diversity and abundance of Commiphora species is found. In between, there are few or no species. Many other plants follow this pattern, Moringa among them. The greatest diversity of Moringa species is found in the tropical dry lowlands of northeastern Africa, especially the area where Kenya, Ethiopia, and Somalia meet. Moringa arborea, borziana, longituba, peregrina, pygmaea, rivae, ruspoliana, and stenopetala all grow in this area. Moringa borziana is the southernmost of the northeast Africa species, growing west of Mombasa in southeastern Kenya. It has never been collected in Tanzania as far as I know. The westernmost of the northeast African species is M. stenopetala, which grows in the Kenyan Rift Valley in northwestern Kenya. To the west of the Kenyan drylands lie the wet forest of the Congos and Gabon. No moringas there. To the south we only find moringas again in souther Angola and northern to central Namibia, as well as in Madagascar. What gives? What causes this pattern, in which related dryland plants are found in southwestern and northeastern Africa but nowhere else? Graduate student John Zaborsky, in Ken Systma's lab at the University of Wisconsin-Madison, is using Moringa samples from the International Moringa germplasm Collection, plus a bunch of other plant lineages, to examine this issue. John says It is hypothesized that an African Arid Corridor existed across the humid, wet interior of Africa numerous times in the past that allowed these plants to move north and south. I want to test whether the divergence times of these taxa align with the known/hypothesized timing of the corridor or whether long distance dispersal can explain these distributions. John plans to obtain as many samples as possible from plant groups that have species growing in both northeast and southwestern Africa. He can then reconstruct the patterns of relationship between the species based on similarities in their DNA sequences. Given some ideas about how fast the DNA of these groups mutates, he will be able more or less to estimate when the northeast-southwest splits occured. If the splits coincide with moments when the African Arid Corridor was available, then this evidence will suggest that the plants migrated along it. If he finds that the splits do not coincide, this might suggest that long-distance dispersal is the likely agent, e.g. birds carrying seeds from northeast to southwest Africa. Because of its classic northeast-southwest distribution, Moringa is a key group for John's study. We sent him samples of M. borziana, M. concanensis, M. drouhardii, M. longituba, M. oleifera, M. ovalifolia, M. peregrina, M. rivae, M ruspoliana, and M. stenopetala. The crucial split in the family occurs between the southern species (M. drouhardii, M. hildebrandtii, both Madagascar, and M. ovalifolia, of Namibia) and M. stenopetala + the rest of the genus (northeast Africa, Arabia, and the Indian subcontinent. Long-distance dispersal seems unlikely for Moringa given that the seeds are very large and have adaptations for wind dispersal (the wings on the seeds of most species) or possibly even water (the spongy tissue in M. stenopetala seeds), which would only get them relatively short distances. These features also make them unlikely candidates for ingestion and later excretion by birds. They germinate very fast, making long distance floating in salt water seem unlikely. So my bet is that the M. ovalifolia-rest of the genus split falls at a time coincident with the Africa Arid Corridor. We'll keep an eye on John's progress and see what he finds! ReferencesOlson, M. E. 2002. Combining data from DNA sequences and morphology for a phylogeny of Moringaceae. Systematic Botany 27(1): 55-73. pdf
Verdcourt, B. 1985. A synopsis of Moringaceae. Kew Bulletin 40: 1-23. |
AuthorDr. Mark E. Olson is a researcher at Mexico's national university and an expert on the biology of the genus Moringa Archives
November 2018
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