Systematics and classification
The genus Hyphaene is apparently composed of 8 spp. (Dransfield et al. 2008, Stauffer et al., 2014, Stauffer et al., 2018)
This palm group was first described by the celebrated German physician and botanist Joseph Gaertner (1732-1791), in his publication De Fructibus et Seminibus Plantarum (1788) (Fig.1). At that time the species Hyphaene coriacea was described as the first taxon within the genus.
Fig. 1. Original description of the genus Hyphaene in De Fructibus et Seminibus Plantarum (1788).
Important contributions in the systematics of the group were carried out by two German botanists in palm science. The first one is the Bavarian palm expert Carl Friedrich Philipp von Martius (1794-1868, Fig. 2), who contributed with the description of several taxa in Hyphaene (i.e. H. petersiana) and made some generic transfers, in particular from the genus Corypha. The botanist and also gardener Hermann Wendland (1825-1923, Fig. 2) described also many important taxa in the group (i.e. H. compressa, H. macrosperma).
Fig. 2. Carl Friedrich Philipp von Martius (Photo courtesy of Botanische Staatssammlung München) and Hermann Wendland (Photo courtesy of Landeshauptstadt Hannover, Fachbereich Herrenhäuser Gärten)
The last taxonomic treatment of Hyphaene was published 90 years ago by Beccari (1924), who interestingly never saw Hyphaene in the wild (Fig. 3). Taxonomical notes for some species were proposed by Furtado (1967, 1970a, 1970b, 1970c), who most probably only had seen H. dichotoma in India (Fig. 3). Working almost exclusively with herbarium material, these authors proposed more than 2/3 of the taxonomic names associated to the genus, most of these to the ranks of species and subspecies.
Some notes on the West African species were offered by Chevalier and Dubois (1938), and a partial treatment for the genus including the East African species was published by Dransfield (1986). Recent publications by Stauffer et al. (2014) and Stauffer et al. (2018) briefly update our knowledge of the tropical African taxa. The number of currently recognized synonyms for some taxa is impressive (H. compressa: 33; H. coriacea: 24; H. petersiana: 21; H. thebaica: 17), which reveals the tortuous taxonomic and nomenclatural history of the genus and highlights the urgent need to re-evaluate the status for most of the names therein included. A complete revision of H. guineensis was undertaken by van Valkenburg and Dransfield (2004), clarifying the taxonomic identity of this palm and providing data on its ecology and distribution.
Fig. 3. The Italian botanist Odoardo Beccari (1843-1920), left, and the Indian botanist Caetano Xavier Furtado (1897-1980), right, described most of the taxonomic diversity in the genus Hyphaene. Photo of OB courtesy of Riccardo Baldini (Florence Herbarium).
An unequivocal fossil of Hyphaene (H. kapelmanii A. D. Pan, B. F. Jacobs, J. Dransf. & W. J. Baker) was described by Pan et al. (2006, Fig. 4) from a tuffaceous ironstone deposit of Late Oligocene age (28-27 Mya) in north-western Ethiopia. A petrified palm petiole (Palmocaulon hyphaenoides) showing similarities with the currently recognized H. dichotoma was described by Shete & Kulkarni (1980) from the Indian Deccan Intertrappean of Maharashtra State. Endocarps supposed to be from the earliest Cretaceous (Aptian) of Egypt are compared to Hyphaene by Vaudois-Miéja and Lejal-Nicol (1987), although one endocarp looked notably Hyphaene-like. Nevertheless, an Aptian age for the formation in which these fossils (Hyphaeneocarpon aegyptiacum) were found is questionable and may be much younger (Schrank, 1992; Dransfield et al., 2008).
Fig. 4. Fossil petiole of Hyphaene kapelmanii A. D. Pan et al. from a tuffaceous ironstone deposit of Late Oligocene age (28-27 Mya) in north-western Ethiopia. Note the characteristic spines on the petiole margins, typical of Hyphaene palms. Photo courtesy of Dr. Aaron Pan (Don Harrington Discovery Center, USA).