Guettarda includes about 110 species of woody, erect or lianescent shrubs and trees. This genus can be recognized in Guettardeae by the combination of details of its leaf venation pattern; axillary cymose inflorescences; bisexual flowers; usually 5-or 6-lobed corollas with a well developed tube; corolla lobes that are imbricated in bud; and fruits with 1 pyrene that is generally 2- to 6-locular, subglobose to oblate, and smooth. In addition, Guettarda is characterized by a woody habit; a lack of raphides in the tissues; persistent or deciduous, usually interpetiolar stipules; sessile or shortly pedicellate flowers with an unusual distylous arrangement, as explained below; white to pale green, cream or pink corollas; drupaceous, juicy, usually purple to purple-black fruits; and cylindrical seeds. The flowers are usually fragrant with an odor similar to Gardenia. Guettarda is mainly found in the Neotropics, but also has one species, Guettarda speciosa, that is widely distributed on tropical seacoasts across the Pacific and the Indian Ocean to East Africa. Within the Neotropics, Guettarda has centers of diversity in Mexico and northern Central America and Brazil. The most commonly collected, widespread species is Guettarda elliptica.
The higher-order leaf venation of Guettarda is generally visible on the abaxial leaf surface, and has a markedly regular and distinctive arrangement with the quaternary veins closely reticulated within larger areas between the tertiary veins to form small, regular, generally square areoles.The corollas are generally 5-6-merous, but a few species have flowers with more lobes, notably Guettarda speciosa with striking 8-9-merous flowers.
At least some species of Guettarda are distylous with a distinctive arrangement (Richards & Koptur, 1993). The floral biology of Guettarda scabra and Guettarda speciosa was found to be distylous with two flower forms that differ in relative rather than specific position of the anthers and stigmas. The anthers of these flowers are positioned near or at the mouth of the corolla tube in both forms, while the stigmas vary in position: the stigmas are held next to or just above the anthers in the long-styled form and below the anthers, near the middle of the corolla tube, in the short-styled form. Richards and Koptur (1993) also documented differences in stigma shape between the two floral forms.
Guettarda has not been studied as whole. It has been treated floristically in several regions, and the taxonomies there are followed here (Borhidi et al. 2017; Liogier 1995; Adams 1972; Lorence et al., 2012; Taylor et al. 2004, Steyermark, 1972; Brazil Catalogue). Several species from Hispaniola and Cuba were described based on sterile specimens, and deserve further evaluation.
The classic circumscription of the Guettarda has varied and narrowed over the years. This genus was long treated as a diverse pantropical group found from the Indian Ocean to South America, with a notable center of diversity in the western Pacific and southeast Asia. The identity and circumscription of Guettarda were studied with molecular data by Achille et al. (2006), who found it was extenstively polyphyletic and, to a large degree, characterized by common morphological traits in Guettardeae. Achille et al. concluded by characterizing Guettarda as having bisexual flowers and including in it only Neotropical species plus Guettarda speciosa. They referred the Paleotropical species, which are dioecious, to Antirhea, Bobea, and potentially Guettardella. Their Neotropical species sampling was limited by the technology of the times and not extensive, but they found the single Guettarda speciosa well nested within a moderately supported clade of Antillean Guettarda. Achille et al. 2006 also noted that some other Neotropical species in their analysis were placed on two other clades, and these have since been separated in Stenostomum and Tournefortiopsis.
Guettarda has been circumscribed until recently in the Neotropics to include Tournefortiopsis, which is (as with most other Guettardeae genera) generally similar. Tournefortiopsis can be separated by its corolla lobes that are valvate-induplicate in bud and pyrenes that are longitudinally ridged and apically prolonged into several horns (Taylor & Berger, 2021). Guettarda is also similar to Pittoniotis, which has lineolate higher-order venation and homostylous flowers. Guettarda is also similar to Chomelia, which has valvate or valvate-induplicate corolla lobes and higher-order leaf venation with various arrangements but not forming closely set quadrangular areoles. Guettarda is also similar to Stenostomum, and these seem to be distinct lineages (Achille et al., 2006) but their diagnostic features remain to be confirmed; at present, Guettarda appears to differ in its pyrenes that are solid in the center, vs. with a central air space or locule in Stenostomum, and in being placed on a separate clade by molecular data.
Several species of Guettarda were originally described in Laugieria by Jacquin and this name has various confusions. This name was published with this spelling by Jacquin in 1760, but then cited shortly afterward by Linnaeus in 1767 with the variant spelling "Laugeria". That variant spelling has been more widely used, and considered simillar enough to the same as Jacquin's original spelling. Linnaeus's name has also confused with Vahl's use of this name: the name Laugeria was used for a separate species by Vahl in 1797, but not validly published by him. Vahl's name was later adopted by Hooker in 1873, but that is generally treated as a later homonym of Jacquin's name.
Author: C.M. Taylor. The content of this web page was last revised on 26 February 2022.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml