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Failure to Confirm the New African Diploid Baobab, Adansonia kilima: New DAPI karyotype.Cron.html
Cron GV, Karimi N, Glennon KL, Chukwudi A, Udeh, E, Witkowski TF, Venter SV, Assogbadjo AE & Baum D.(2016)
Taxon 65(5) 1037-1049

Commentary on Cron et al. (2016): If a new tree species has gone unrecognised in plain sight for decades, it is to be expected that its eventual recognition will not prove to be easy or straightforward. In this paper, David Baum and colleagues completely reject the hypothesis that there is an unrecognised African diploid baobab, using similar techniques to those first used to define the new species, with a beautiful crowning observation of a DAPI-stained tetraploid karyotype, purportedly from the diploid species, that no doubt charmed the reviewers at Taxon. Without any corroboration, we cannot be sure that the striking sample does not actually come from the tetraploid species, A. digitata, that is found in the same locality as the target sample. In view of the overlap between measurements already published for these two very similar species, as well as the difficulty in always linking a field identification securely to complex laboratory investigations like DNA sequencing and DAPI karyotyping, questions can arise that can cloud an apparently definitive picture like the blue karyotype.

There are therefore some unanswered questions in this paper. For example, the large karyotype illustrated may be a misidentified specimen of A. digitata from the Venda, on the edge of the African baobab distribution where A. digitata and A. kilima were both found together, unlike highland stands. The choice of a Type specimen for A. kilima from this mixed Venda population was a mistake by the original investigators, inexperienced in botanical lore, who had been advised that this would be a convenient location because of its easy access by road, instead of a more secure location from a pure stand of A. kilima in the Tanzanian highlands.

Pollen Size Confirms Original Findings: Another major question concerns the data on pollen that have been collected in the study. These data confirm the original study by showing much smaller pollen in A. kilima than in A. digitata, as expected for the contrast in DNA content of diploids and tetraploids respectively. This observation is not consistent with their own results of flow cytometry and DAPI karyotyping in the same study, and could be explained by the fact that they give no determinations of both karyotype and pollen on the same samples, with the risk of possible misidentification already mentioned. It is also hard to justify the subsequent exclusion of these pollen -size data from the later analysis using the collective data set, when they show a contrast central to their study. Leaving out these data, without explanation, could explain the lack of differentiation in their Fig. 1.

Resolution of these difficulties would require a variety of measures on the same tree, not separate pollen, karyotype, and other measurements of different samples. In the original study, stomata, pollen, karyotype, nITS sequence, floral characterisation and biogeography determinations were sometimes all carried out on the same tree to fix its identity. In contrast, their presented, single DAPI-stained tetraploid karyotype is very beautiful, but might be derived from A. digitata instead of A. kilima, without individual corroboration from the any of the other relevant quantitative features that have helped to define A. kilima.

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