Statistical analysis (version 1.0 checklist)

A patch of vegetation growing near the summit of Domboshawa hill. Note the very marked run-off stains. Taken on: 17th August, 2003 at 12.05 p.m.

Overall totals

This first table shows the number of vascular plants in the flora of Zimbabwe counted from the version 1.0 checklist published on this site on 3 March, 2003.

Notes:

By the term taxa we mean taxa at the rank of species or lower, i.e. species, subspecies, varieties and in a very few cases, forms. Also included here are hybrids and "numbered" species which have not yet been named.

The table shows that there are 6225 taxa in the Zimbabwean flora. This compares with a figure of 5428 taxa given in Gibbs Russell (1975). One may speculate that over the 28 years since that paper, the number of taxa has increased (by 14,7%) as a result of more extensive fieldwork and collection, taxonomic research (which often seems to increase the number of recognised taxa) and because of the arrival of new alien species.

It may also be seen that the number of Pteridophytes is 4.7% of the total vascular plant flora. The number (293) has increased by 30,8% compared to the figure of 224 in Gibbs Russell (1975).

In the table below is the breakdown of the spermatophytes into the gymnosperms and the angiosperms and in addition the split of the angiosperms into monocotyledons and dicotyledons.

Note in the table above that the angiosperms row is a subtotal of the monocotyledons and dicotyledons row.

It may be noted that Zimbabwe is poor in gymnosperms with a high proportion of those represented being introductions.

Of the angiosperms, monocotyledons account for 28% of the taxa and dicotyledons for 72%. The proportion of monocotyledons which are introductions (4.2%) is considerably lower than the proportion of dicotyledons (7.1%).

Largest families

The families with more than 100 taxa are in the following table. The grasses have the biggest total on this measure followed by the papilionoid legumes and the composites.

However, these relative positions do depend on which particular concept of each family is being followed. If, for example, we combine the Caesalpinioideae and the Mimosoideae with the Papilionoideae and treat them as one family, the Fabaceae, then that family becomes the biggest with a total of 709 taxa.

Another example of the same point is the Liliaceae. These were the 9th largest family in the flora with 159 taxa in Gibbs Russell (1975); now they have been fragmented into a number of small families and do not feature on the list at all.

Distribution information

Another set of data which can be analysed is the distribution of taxa within the 5 divisions of Zimbabwe, N,W,C,E and S.

In order to carry out this analysis, the number of occurrences of each possible combination of the 5 divisions was obtained.

The results are set out in the next table.

The total of 6182 is lower than the 6225 given earlier because there are a number of taxa whose distribution is not known or is doubtful and such cases have been excluded.

The richest division by number of taxa is the one with the smallest surface area, division E. It has 4362 taxa, far more than any of the others. This is presumably so because of the wide range of habitat resulting from its exceptional altitudinal range, the range of rainfall from exceptionally wet to very dry, the varying geology and the endemism of its mountain ranges.

The next richest is the Central Division with 3172 taxa. Again, this area has quite a wide range of altitude, rainfall and habitat. It is also I suspect helped by having Harare with its concentration of botanical expertise and possibly alien plants.

The poorest is the Southern Division with 2721 taxa.

Mark Hyde

28 October 2003