Bathysa includes at perhaps 15 species of shrubs to robust trees with multiflowered terminal inflorescences and subglobose capsular fruits. This genus is characterized by petiolate, generally elliptic to obovate, opposite leaves; interpetiolar or calyptrate stipules that are caducous; broadly pyramidal to rounded, terminal, pedunculate inflorescences with numerous small, protandrous, 5-merous flowers; shortly funnelform to campanulate corollas with the lobes thinly imbricated in bud; and subglobose septicidal capsules with numerous angled seeds. The stipules are interpetiolar and triangular in all but two of the species, as discussed in more detail below. The flowers are fragrant, and have white to green corollas with barbate throats and pubescent filaments. The flower merosity often varies within a species, with the flowers variously 4- and 5-merous on a single plant (e.g., Steyermark, 1974: p. 407, fig. 65d). Bathysa has been described by previous authors as sometimes having petaloid calycophylls, but those species are no longer included in this genus. The corollas are densely pubescent in the tube at and sometimes above the stamen insertion. The corolla lobes are so thinly imbricated they can appear valvate unless studied carefully. The anthers and fleshy stigmas are well exserted from the corolla, and the styles and abaxial surfaces of the stigmas are often densely strigose or hirtellous. The capsules are stiff-textured to woody and the valves characteristically remain attached to the inflorescence after dehiscence. Bathysa has a relatively broad geographic distribution for its number of species, with generally few species in a region except there is a center of species diversity in eastern and southeastern Brazil.

Delprete (1996, 1999) reviewed the group of genera that includes Bathysa and clarified the separation of this genus with respect to some of those genera, in particular Chimarrhis, and transferred two species from Chimarrhis to Bathysa. Subsequently Kainulainen et al. (2010; as Condamineeae) using molecular sequence data found Bathysa to belong to the Tribe Dialypetalantheae, which also included many of the other genera studied by Delprete. Kainulainen et al. found Bathysa as it had been circumscribed to be polyphyletic, and they separated some of its species into Schizocalyx. They did not sample Bathysa comprehensively, and noted that the two species transferred into this genus by Delprete may deserve re-evaluation as to their classification here, Bathysa bathysoides and Bathysa perijaensis. Bathysa was studied in Brazil by Germano Filho (1998), who presented descriptions and illustrations of the species found there. Further studying the characters clarified by Kainulainen et al., Taylor & Maldonado (2023) clarified its separation from Elaeagia and transferred several species from that genus to Bathysa.

Species of Bathysa have been separated for some time based in part on the presence vs. absence of pubescence on the filaments (Schumann, 1888; Germano-Filho, 1998); however the filaments can usually be considered pubescent at least at the base, where dense pubescence is found on the corolla and sometimes on the base of the filaments, and authoritatively identified specimens seem to show variation in this feature within several species. The characters of Bathysa bathysoides and Bathysa perijaensis basically all agree with Bathysa as circumscribed by Kainulainen et al. (2010), as noted in that work. These two species both have calyptrate stipules, while triangular interpetiolar stipules are found in all the other species now included in Bathysa; however this varition in stipule form is found within several genera that are well supported as monophyletic. Bathysa bathysoides and Bathysa perijaensis also have corollas with relatively long tubes and short lobes, in contrast to the corollas of other species of Bathysa, but such variation in corolla form is also found in other general that are clearly monophyletic.

Bathysa is similar to Chimarrhis, which has axillary inflorescences, protogynous flowers, and stipules that are markedly twisted in bud. Schizocalyx differs from Bathysa in its corolla lobes that are convolute in bud and loculicidal capsules (Kainulainen et al., 2010; Taylor et al., 2011); the species previously included in Bathysa with petaloid calycophylls are all now included in Schizocalyx. Bathysa has also been confused with Elaeagia, which has stipules with two intrapetiolar segments and loculicidal capsules. Bathysa is also similar to Warszewiczia, which has protogynous flowers. The generic classification here of Bathysa multiflora needs confirmation, and Elaeagia mollis is a species of Bathysa.

Author: C.M. Taylor
The content of this web page was last revised on 19 March 2023.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

• Delprete, P. G. 1999. Rondeletieae (Rubiaceae)—Part I (Rustia, Tresanthera, Condaminea, Picardaea, Pogonopus, Chimarrhis, Dioicodendron, Molopanthera, Dolichodelphys, and Parachimarrhis). Fl. Neotrop. Monogr. 77: 1–226.
• Kainulainen, K., C. H. Persson, T. Eriksson & B. Bremer. 2010. Molecular systematics and morphological character evolution of the Condamineeae (Rubiaceae). Amer. J. Bot. 97(12): 1961–1981.
• Germano Filho, P. 1998. Estudos taxonômicos do gênero Bathysa C. Presl (Rubiaceae, Rondeletieae), no Brasil. Rodriguésia 50(76–77): 49–75.
• Taylor, C. M., D. A. Neill & R. E. Gereau. 2011. Rubiacearum americanarum magna hama pars XXIX: Overview of the neotropical genus Schizocalyx (Condamineeae) and description of two new species. Novon 21(4): 496–507.
• Steyermark, J. A. 1974. Rubiaceae. 9(1–3): 7–2070. In T. Lasser (ed.) Fl. Venezuela. Fondo Editorial Acta Científica Venezolana, Caracas.
• Delprete, P. G. 1996. Notes on calycophyllous Rubiaceae. Part I. Morphological comparisons of the genera Chimarrhis, Bathysa, and Calycophyllum, with new combinations and a new species, Chimarrhis gentryana. Brittonia 48(1): 35–44.
• Schumann, K. M. 1888. Rubiaceae. 6(6, 1): 1–124, t. 68–93. In C. F. P. von Martius (ed.) Fl. Bras. F. Fleischer, Monachii & Lipsiae.
• Taylor, C. M. & C. B. Maldonado Goyzueta. 2023. Rubiacearum Americanarum Magna Hama Pars L: New Species, Combinations, and Notes for Some South American Genera of Dialypetalantheae (Former Condamineeae). Novon 31(1): 36-70.