Araujia Brotero (1817: 62)

Rapini, Alessandro, Pereira, Jorge Fontella & Goyder, David J., 2011, Towards a stable generic circumscription in Oxypetalinae (Apocynaceae), Phytotaxa 26, pp. 9-16 : 10-11

Araujia Brotero (1817: 62) . Type: A. sericifera Brotero (1817: 62 ; t. 4–5).

Physianthus Mart. in Martius & Zuccarini (1824: 53). Type: P. albens Mart. in Martius & Zuccarini (1824: 54; t. 32).

Morrenia Lindley (1838: 71) . Type: M. odorata ( Hooker & Arnott 1834: 294) Lindley (1838: 71) . Synon. nov.

Lagenia Fournier (1885: 293) . Lectotype (here designated): L. megapotamica ( Sprengel 1827: 111) Fournier (1885: 293) .

Stuckertia Kuntze in Post & Kuntze (1902: 541) Ξ Choristigma Kurtz ex Heger (1897: 443) , hom. post. [ non ( Baillon 1862: 117) Baillon (1892: 454). Olacaceae ]. Type: C. stuckertianum Kurtz ex Heger (1897: 443) . Synon. nov.

Hickenia Lillo (1919: 422) . Type: H. s calae ( Hicken 1918: 306) Lillo (1919: 423). Synon. nov.

Note:—Historically, Araujia and Morrenia have been considered closely related genera but treated as distinct based on subtle differences such as the thickness and consistency of style-head and the corolla shape ( e.g., Goyder 2003, 2004). A hyaline appendage on the corpusculum was also used to recognise Araujia , however, similar appendages are found in other genera of Oxypetalinae —for instance, Oxypetalum appendiculatum Martius in Martius & Zuccarini (1824: 48; t. 30)—and, on the other hand, this character state is not present in A. plumosa Schlechter (1895: 449) . Curiously, the latter species shares other attributes with species of Morrenia , such as the fimbriate anther appendage and contorted anther wings ( Goyder 2003) and, phylogenetically, it is more closely related to M. odorata than to A. sericifera , a relationship highly supported based on plastid data ( Liede-Schumann et al. 2005). Araujia and Morrenia are small genera (with four and eight accepted species, respectively), they are difficult to distinguish as currently defined, and the recognition of Morrenia makes Araujia paraphyletic. The synonymisation of Morrenia under Araujia will certainly provide a more stable classification, based on a monophyletic, easily recognisable group of reasonable size and geographic integrity.

Physianthus and Lagenia have been treated in the synonymy of Araujia since Decaisne (1844) and Schumann (1895), respectively. The monotypic Hickenia was transferred to Morrenia by Goyder (2001), and Stuckertia treated as a synonym of Morrenia by Goyder (2003). They are treated here within the expanded concept of Araujia . Based on this circumscription, Araujia comprises twelve South American species occurring in northern Argentina, southern Bolivia, Paraguay, southern and south-western Brazil, and Uruguay, with a centre of diversity in the Chaco.

Below, we provide the combinations for seven of the eight species (and one subspecies) of Morrenia ( Goyder 2003) in Araujia ; Morrenia stormiana ( Morong 1893: 161) Malme in Chodat & Hassler (1903: 65) was described originally under Araujia . We also designate lectotypes for three species and indicate a new synonym.