Today’s post will be all about the wonderful Fabaceae. Broadly defined, the Fabaceae is the third largest family in the world in terms of number of species, but tied first (with the Poaceae, or grasses) in terms of ecological and economic significance. The Legume or Pea family (as it is commonly referred to) contains over 18 800 species in 630 genera, behind only the Asteraceae (asterids) and the Orchidaceae (orchids). Many of these species provide staple foods, either directly (e.g. pulses, beans and peas) or indirectly (e.g. alfalfa or lucerne, which provides grazing or fodder for cattle). The term “faba-” itself comes from Latin for “bean”. The reason for the high nutritional value of legumes is that they contain nitrogen-fixing bacteria (known as Rhizobia) in nodules in their roots, which allows them to be self-nourishing.
In southern Africa, the Fabaceae (again, broadly defined) contains more than 280 species, many of which are important tree species. Why do I keep mentioning “broadly defined”? The Fabaceae is such a large family that some taxonomists split it into three “narrowly defined” families: the Papilionaceae (or Fabaceae, narrowly defined), the Caesalpiniaceae and the Mimosaceae.
The Fabaceae (narrowly defined) is still a very large family, containing approximately 133 tree species in southern Africa. Many people will be familiar with this group, as most species are instantly recognizable by their butterfly-shaped flowers (“papillon” is French for “butterfly”). The flowers have a keel (shaped like a boat), an uppermost “banner” and two side lobes (or wings). Erythrina and Virgilia are commonly encountered trees in southern Africa.
The Caesalpiniaceae (or flamboyant family) is the nineth largest group of trees in southern Africa, containing approximately 50 species. The region that I grew up in along South Africa’s south coast has one particularly spectacular ornamental tree species from this group: Bauhinia galpinii, also known as “the pride of the Cape”.
According to Coetzer (University of Pretoria) the popular name for this tree species was first used in November 1889 by E.E. Galpin:
The popular name of Pride of the Cape may have been used for the first time in November 1889 by Galpin, a dedicated plant collector, while he was introduced to this plant in the Cape during a botanical excursion. During the flowering periods of the plant that stretch from October to May (June), the flowers with their brick to orange-red color are very noticeable. Therefore, one can understand why it made a big impression on Dr. Galpin made when he first observed and collected the plants.Coetzer (1974) Veld and Flora
The species was given it’s scientific name in England by Dr. N.E. Brown who studied all available specimens of the “Flame of the Cape” and placed it under the genus Bauhinia L. “mainly on the basis of the shape and hand-shaped bearing of the leaves”. Dr. Brown was also the person who decided to honour Dr. Galpin, publishing his description of Bauhinia galpinii in the London Gardener’s Chronicle in June 1891. As a side note, the two common names should again make one think twice about the value of popular names for a species. I have mentioned this before in a previous post, but Coetzer, writing about Bauhinia galpinii, shared similar sentiments:
In the vernacular, where the more popular names originate, no scientific facts such as morphological features are taken into account when giving a name. The names usually differ from region to region and in many cases the same plant has more than one popular name. These many names for the same plant create confusion and make communication very difficult.Coetzer (1974) Veld and Flora
Of the three narrowly defined families of the Fabaceae, the Mimosa family contains the most number of tree species in southern Africa (about 133 species). Many of these species will be recognisable to most people who have ever gone on safari as the thorn trees with small yellow pom-pom-like flowers that obscure their views of charismatic herbivores. Whether you refer to them as Acacia, Vachellia or Senegalia will depend on your knowledge of taxonomy (a story for another time)…
With these three narrowly-defined plant “families” we have covered the second (Fabaceae), third (Mimosaceae), and nineth (Caesalpiniaceae) largest tree families in southern Africa. Added to the Rubiaceae, we’re off to a good start in covering the tree flora of the region.