Monanthotaxis

Hoekstra, P. H., Wieringa, J. J., Maas, P. J. M. & Chatrou, L. W., 2021, Revision of the African species of Monanthotaxis (Annonaceae), Blumea 66 (2), pp. 107-221 : 107-108

History of Monanthotaxis

The oldest specimens known that are now attributed to Monanthotaxis were collected by Adam Afzelius, one of Linnaeus’ apostles, in Sierra Leone in 1795. It took more than 200 years before these specimens were identified as M. barteri (Baill.) Verdc. Compared to other large genera of Annonaceae , it has taken a long time for the species in Monanthotaxis to be recognized as a coherent group of similar species representing a genus. In 1890 Baillon described the genus Monanthotaxis with the sole species M. congoensis Baill. , with a single whorl of petals and stamens as distinguishing characters ( Baillon 1890). At that point, almost 30 species now classified in Monanthotaxis , had already been described in other genera ( Clathrospermum Planch. ex Benth. , Guatteria Ruiz & Pav. , Oxymitra (Blume) Hook.f. & Thomson , Popowia Endl. , Unona L.f. and Uvaria L.), yet Baillon did not transfer any of these into the genus he described. As a matter of fact, Baillon described several species currently placed in this genus as members of Bocagea A.St.Hil. , Clathrospermum , Popowia and Unona . Still in 1969 the genus was portrayed as “a small African genus comprising four species”. ( Le Thomas 1969).

After Baillon several additional species were described culminating in the revision of African Annonaceae by Engler & Diels (1901). In that revision more than 45 names relevant for this revision were included in the genera Monanthotaxis , Oxymitra , Popowia and Unona , 30 of which are currently accepted species in Monanthotaxis .

In 1932 Exell described the new genus Enneastemon Exell ( Exell 1932) , which he stated was related to the genera Monanthotaxis and Popowia . It differed from Popowia and Monanthotaxis in the arrangement of the petals. For his treatment of the Annonaceae in the Flora of Tropical West Africa, Keay (1953) synonymized Clathrospermum with Enneastemon based on the fact that both genera had the same petal aestivation. Keay & Boutique (1953) proposed to conserve Enneastemon over Clathrospermum based on four reasons, including that the name of Clathrospermum had not been used in 50 years, while Enneastemon already had been adopted in several floras, because Clathrospermum was incorrectly diagnosed by a single flower, which no longer exists and to avoid at least 9 specific transfers ( Keay & Boutique 1953). This proposal got rejected ( Rickett 1958), upon which Wild (1959) proposed a second time to conserve Enneastemon against Clathrospermum stressing out the fact that 4 modern floras had used the name Enneastemon and that Keay had consulted many colleagues working on the African flora. This proposal got accepted ( Rickett 1961). Polyalthia section Oxymitra Blume was raised to genus level in 1855 by Hooker & Thomson. However, the name Oxymitra (Blume) Hook.f. & Thomson had been preceded by the moss genus Oxymitra Bisch. ex Lindenb. A proposal to conserve the Annonaceae genus name Oxymitra over the moss genus name Oxymitra got rejected ( Pichi-Sermolli 1954). Fries (1959) considered Oxymitra a synonym of Richella A.Gray ( Gray 1852) , and transferred the recognized species. Subsequently, Van Steenis (1964) examined the types of Richella and Oxymitra and decided that Richella was distinct from Oxymitra based on several characters among which clearly distinct seeds. Therefore, as the name Oxymitra was not available, he reassigned those species to Friesodielsia .

In 1951 Boutique published three new genera: Atopostema Boutique, Exellia Boutique and Gilbertiella Boutique ( Boutique 1951b) .

During the fifties and sixties several important treatments of Annonaceae were published in regional floras ( Boutique 1951 a, Cavaco & Keraudren 1958, Robson 1960, Le Thomas 1969). They all placed the current species of Monanthotaxis in several distinct genera with the majority in Popowia . Verdcourt (1971b) critically revised those genera and concluded that the Asian species of Popowia were distinct from the African species and that the African species were most closely related to Monanthotaxis . He therefore united the majority of African species names of Popowia with Monanthotaxis together with all species of Enneastemon . As the name Enneastemon has priority over Clathrospermum and Monanthotaxis is an older name than Enneastemon , all species were recombined into Monanthotaxis , in which 55 species were then recognized (Verdcourt 1971b). Based on the shape of the stamens Verdcourt (1971b) divided the genus in three subgenera: Monanthotaxis , Neopopowia Verdc. and Neopopowiopsis Verdc. Subsequently, he subdivided the subg. Monanthotaxis into five sections, mostly based on petal aestivation. Verdcourt did not include Friesodielsia into Monanthotaxis as the African species of Friesodielsia have many stamens with thick connective appendages forming a tight polygonal pavement when viewed from above, while his circumscription of Monanthotaxis included only species with less than 40 stamens of which the thecae are visible when viewed from above (Verdcourt 1971b). This classification remained as such for 40 years, till a phylogenetic study ( Guo et al. 2017) using one third of the current species diversity found that most African species of Friesodielsia were paraphyletic with Monanthotaxis and not related to the Asian species of Friesodielsia . In addition, this study showed that the genera Exellia and Gilbertiella clustered within the genus Monanthotaxis . This resulted in the transfer of eight African species names of Friesodielsia to Monanthotaxis as well as the inclusion of the genera Exellia and Gilbertiella ( Guo et al. 2017) .