The circumscription and relationships of this tribe have long been problematic (e.g., Robbrecht & Manen, 2006), but these have been clarified in general with molecular analysis by Manns & Bremer (2010), and with a focus on the Neotroipcal genera using morphological characters, molecular data, and study of the taxonomy and systematics of several component genera by Torres-Montúfar et al. (2020).The list of genera here is based on Manns & Bremer and Torres-Montúfar et al. Part of the problem of separating these tribes has been addressed through study of some of the component genera, which has divided some of broadly circumscribed genera of one tribe with some lineages now placed in the other tribe (e.g., Arachnothryx and Javorkaea, from Rondeletia of Lorence et al. 2012). Guettardeae has a pantropical distribution and is more widespread in the Neotropics, but shows a generally similar geographic pattern of generic diversity to Rondeletieae. Several genera of Guettardeae have notably large species radiations, in the Neotropics Arachnothryx and in the Paleotropics Timonius.
Rondeletieae and Guettardeae were both generally characterized by Torres-Montúfar et al. (2020) by its quincuncial corolla aestivation and "spathulate" corolla lobes, and they noted that some (but not all) genera have a unique combination of fruit and pollen characters. Additionally, both tribes are predominantly woody with a shrub or small tree habit and lack raphides, and the Neotropical genera of Guettardeae have ovaries with one to several seeds on axile placentas in each locule and capsular, indehiscent, and/or drupaceous, sometimes fleshy fruits.
Neotropical genera of this tribe have also been studied taxonomically by Taylor & Gereau (2010) and Taylor & Berger (2021), and selected genera by Borhidi in various works. There are several systematically complex and poorly understood groups or complexes in Neotropical Guettardeae, including Stenostomum, Neolaugeria, and Guettarda. These genera have been studied to some extent in broad molecular surveys by Achille and collaborators (2006a, 2006b, 2010) and Chavez et al. (2021; names of several taxa analyzed not updated to current taxonomy). Those works are informative by largely focussed on Paleotropical groups, so the generic placement of some Neotropical species was also addressed but the overall characters and circumscription of the Neotropical genera not fully clarified.
Author: C.M. Taylor. The content of this web page was last revised on 3 February 2021.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml