Acunaeanthus includes 1 species of shrubs and small trees from western Cuba. It is characterized by its woody habit; medium-sized petiolate leaves with pubescence domatia; persistent triangular stipules; cymose, several-flowered inflorescences borne at the ends of the stems; 4-merous, medium-sized, probably showy flowers; white to pink-flushed, salverform corollas with the lobes imbricated in bud and the throat smooth and glabrous; and obconic, medium-sized capsules that dehisce at the top through the enlarged disk to release numerous small fusiform seeds. A ver good illustration of Acunaeanthus tinifolius was presented by Borhidi et al. (1980: 284, fig. 1, and reprintd but in lesser quality in Borhidi 2017: 36, fig.2). The leaves are distinctive in their blades with the higher-order venation not visible. Acunaeanthus tinifolius has been described twice and is known from various specimens (Delprete, 1999), but cannot be considered frequently collected. 

Detailed recent descriptions of Acunaeanthus and its species have been presented by Borhidi (2017) and Delprete (1999), and these do not agree in all details. Delprete described the stipules as caducous, but Borhid and the review here of specimens found these to be persistent at least with the leaves. Delprete described the leaves as lacking domatia, and some leaves do lack these but they are well developed on other leaves on the type collection. Borhidi (2017) described inflorescences as 3-flowered dichasial cymes, but specimen at MO shows more complex arrangement, similar to that noted by Delprete (1999), with the flowers borne in groups of 3--7, some axes dichasial but others apparently shortly monochasial, and the flowers variously sessile to apparently pedicellate (depending on interpretation, these are separated on pedicels or axes of the cyme). 

Few flowers were seen in this current review and, apparently, by Borhidi (2017) and Delprete (1999), and whether Acunaeanthus tinifolius is distylous or not cannot be confirmed. The flowers were described by Borhidi et al. (1980) and Borhidi (2017) as 4-merous, which agrees with specimens seen in this review. However, Delprete (1999) described them as 4-5-merous; similar variation is found in individual species of some other Rondeletieae genera so this is not unexpected. Borhidi et al. (1980: 283-284 286, tab. II) detailed and illustrated the pollen, which they described as 3-colpate, globose, and with a granular surface; see that reference for more details. 

The form of the capsule of Acunaeanthus is distinctive, with an enlarged, rounded, apparently thick-textured disk elongated as the fruits mature and dehiscence beginning through the disk. The type of dehiscence of these capsules has been described differently by different authors, however, and the stages of dehiscence were illustrated and noted briefly by Borhidi et al. (1980: 284, Fig. 1h-i) but only generally sketched out in less detal by Borhidi (2017). The capsules of Acunaeanthus have been considered variously as loculicidal (Borhidi et al., 1980; Borhidi, 2017; Torres-Montúfar et al., 2020) and as septicidal (Delprete, 1999), and each of these seems to accurately describe a stage of the process. The capsules appear to first open narrowly at the top, through the disk (Borhidi et al., 1980: fig. 1h; Wright 2682, S specimen S05-440, uppermost fruit), into 2 and then very quickly into 4 short valves. Borhidi described this initial dehiscence as loculicidal, which does not conflict with materials seen; however, whether this first opening iof the capsules s loculicidal or septicidal or these are simultaneous is not completely clear on the material seen. Subsequently, the capsule splits septicidally into 2 segments, and old fruits with this form are represented on some of the other duplicates of Wright 2682. Probably field observations will be needed to further clarify what actually happens. In either case, loculicidal or septicidal, the initial opening of the capsule through the enlarged disk is unique in Rondeletieae. 

In general aspect Acunaeanthus is similar to Roigella, as noted by Borhidi (1981), but Roigella can be separated by 5-6-merous, narrower triangular calyx lobes, the corolla glabrous in the throat, and smaller capsules, 12--15 mm long, with the disk not enlarged. In spite of the general similarity of these two genera, Torres-Montúfar et al. (2020) did not find them closely related within Rondeletieae. Acunaeanthus  has been provisionally included in several Antillean genera. Rondeletia can be separated by its fruits which are subglobose capsules that are deeply loculicidal. Mazaea has been variously characterized but today is narrowly circumscribed to include only one (Borhidi, 2017) or two (Delprete, 1999; Torres-Montúfar et al., 2020) species, which have different corolla morphologies but both can be separated by their axillary inflorescences, shallowly lobed calyx limbs, and ovaries and fruits with 1--2 seeds per locule. 

Acunaeanthus has sometimes been cited with variant spellings, such as "Acunaneanthus" and "Acuneanthus". 

Author: C.M. Taylor The content of this web page was last revised on 9 July 2021.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

• Borhidi, A. L., M. Járai-Komlódi & M. Moncada Ferrera. 1980 [1981]. Acunaeanthus, a new genus of Rubiaceae. Acta Bot. Acad. Sci. Hung. 26(3–4): 277–287.
• Borhidi, A. L., M. Fernández Zequeira & R. Oviedo Prieto. 2017. Rubiác. Cuba 1–494.
• Torres-Montúfar, A., T. Borsch, S. Fuentes-Bazán, J. Gutiérrez & H. Ochoterena-Booth. 2020. It is not a disaster: molecular and morphologically based phylogenetic analysis of Rondeletieae and the Rondeletia complex (Cinchonoideae, Rubiaceae). Pl. Syst. Evol. 306(26): 1–25.
• Delprete, P. G. 1999. The Cuban endemic genera Ariadne, Mazaea, Acunaeanthus, Phyllomelia (Rondeletieae), and Eosanthe (Rubiaceae). Brittonia 51(2): 217–230.
• Borhidi, A. L. & M. Fernández Zequeira. 1981. Studies in Rondeletieae I. A new genus: Roigella. Acta Bot. Acad. Sci. Hung. 27(3–4): 309–312.