Phylogenetics of Hyphaene and Hyphaeninae

The placement of Hyphaene in the palm subfamily Coryphoideae was first proposed by Uhl and Dransfield (1987) and supported strongly in later studies relying on molecular phylogenetics (Dransfield et al., 2008). Modern molecular phylogenies confirm Hyphaene as a highly supported monophyletic group (Bayton, 2005; Asmussen et al., 2006; Baker et al., 2009, Fig. 1), with moderate to high support for a sister-relationship to the monotypic Medemia, endemic to the Egyptian Nubian Desert and north-eastern Sudan, (Bayton, 2005; Asmussen et al., 2006; Baker et al., 2009).

Fig. 1. Phylogenetic position of Hyphaene within Coryphoideae. Strict consensus of the 46 080 trees from the supermatrix analysis of all palm genera (tree length = 15 173, CI = 0.41, RI = 0.62). Values above branches are BPs (>50%). Adapted from Baker et al. (2009).

A new phylogeny for the genus Hyphaene

A new species-level phylogenetic analysis on the genus Hyphaene was recently produced by Camille Christe, Yamama Naciri and Mathieu Perret from the laboratory of the Unité de Phylogénie et Génétique Moléculaires of the Conservatory and Botanic Gardens of Geneva (Figs. 2-5). It is based on NGS techniques and is represented by up to 160 individuals sampled in at least 10 African countries. A simplified working pipeline proposed by Dr. Camille Christe is presented in Fig. 6 and a the new phylogeny is shown in Fig. 7. Several important questions on the systematic relationships within the genus, evolutionary history of the aerial branching growth, typical for some species, and ages of origin and diversification, can be now addressed in a phylogenetic context. Note that the rare north-west Indian species H. dichotoma is not genetically different from the  morphologically closed H. compressa. This striking result was obtained by sequencing DNA extracted from leaves of H. dichotoma collected in India in 1908 and stored in the Kew herbarium.

Fig. 2. Camille Christe and Regine Niba are undertaking most of the lab work associated to the project. The well-equipped laboratory at La Console is ready for the challenging Hyphaene NGS phylogenetic approach.

Fig. 3. Extraction of DNA from some Hyphaene species for which the amount originally extracted was lower than necessary. The extraction room has all the necessary equipments and of course, the technical skills of Regine!.

Fig. 4. Carefull manipulation of the specimens is necessary to extract the DNA. Althought it is straight forward, the protocol is long and requires of full concentration.

Fig. 5. DNA extraction of the first 60 Hyphaene samples. It worked well although some fine-tuning is necessary. 

 Fig. 6. Simplified working pipeline proposed by Dr. Camille Christe (laboratory of the Unité de Phylogénie et Génétique Moléculaires of the Conservatory and Botanic Gardens of Geneva)

Fig. 7. First species-level phylogenetic analysis of the genus Hyphaene has been recently produced by Camille Christe, Yamama Naciri and Mathieu Perret from the laboratory of the Unité de Phylogénie et Génétique Moléculaires of the Conservatory and Botanic Gardens of Geneva. It is based on NGS techniques and is represented by up to 160 individuals sampled in at least 10 African countries. Five species are clearly recognized within the genus, whereas some hybrids individuals, mostly of cultivated origin, could be also detected. On-going analyses will provide critical information on the systematics and evolutionary history of the genus.

Sister relationship of Hyphaene

Available phylogenies support a sister relationship between Hyphaene and Medemia (Fig. 8) within the tribe Hyphaeninae (sensu Dransfield et al., 2008). Medemia (1-2 spp.), longtime believed to be extinct, was rediscovered but the populations remain heavily threatened. This palm is endemic to the Nubian Desert, in the border between Egypt and Sudan. This palm can be distinguish from Hyphaene by its hastula completely lacking and its petioles much less armed than in Hyphaene. More recently Morcote, Raz and Stauffer (Project on African Phytoliths) found morphological differences between the phytoliths of Medemia and those observed in Hyphaene (Fig. 9). Leaf surfaces (presence vs. absence of trichomes) in Borasseae seems to be informative to taxonomically separate some genera and this is a good character to observe in living and herbarium material. Whereas the presence of conspicuos trichomes is evident in Hyphaene and Medemia , they are completely absent in Borassus and Bismarkia (Fig. 10).

Fig. 8 Medemia argun. Growth habit in southern Egypt (Photo Bill Baker); detail of petiole (top right); detail of fruits (bottom-right, specimen at the K Herbarium).

Fig. 9. Phytoliths in Hyphaeninae. Medemia argun (left); Hyphaene coriacea (right). Project "Phytoliths in African Palms" (Gaspar Morcote, Fred Stauffer and Lauren Raz - Universidad Nacional de Colombia, Conservatory and Botanic Gardens of Geneva).

Fig. 10. Leaf surfaces in Borasseae. The presence of conspicuos trichomes is evident in Hyphaene and Medemia, whereas they are completely absent in Borassus and Bismarkia. Upper images were captured with light microscopy whereas lower images were captured with Scanning Electronic Microscopy (Dr. André Piuz, Natural History Museum of Geneva).