The genus Psychotria is found world-wide in tropical regions, and is one of the largest genera of flowering plants in the world with perhaps 1500--2000 species. It is characterized by a generally woody habit, stipules of various forms that are often bilobed and caducous, cymose inflorescences that are usually terminal, generally 5-merous distylous flowers, corollas with the lobes valvate in bud, mostly 2-locular ovaries, ovules solitary and basal in each locule, drupaceous fruits with usually 2 pyrenes that lack pre-formed germination slits, and seeds coats with an alcohol soluble red pigment. Psychotria has centers of diversity in the northern Neotropics, in tropical Africa, in Madagascar, in southeast Asia, and in the Pacific region. It has 100 or more species in each of these regions, and lacks any pantropically distributed species. Psychotria has notable species radiations one several humid tropical islands, including Cuba, Hispaniola, Madagascar, New Caledonia, and Tahiti.
The information here gives a general overview of the systematics and morphology of this genus, and then detailed information about mainly the Neotropical species plus some species from Madagascar studied by Taylor and collaborators (Taylor, 2020; Taylor et al., 2020; Taylor et al. 2023). For more comprehensive information in Tropicos about the Malagasy species of Paleotropical Psychotria, see the Madagascar Catalogue page for this genus (go to upper right of web page and click on "Chose Project", then choose "Madagascar"). For the African and Malagasy species with bacterial nodules, the symbotic Burkholderia bacteria in the nodules were inaccurately described as fixing nitrogen by (Taylor, 2020) and Taylor et al. (2020), but these do not actually fix nitrogen. The function of the symbiosis is not entirely clear, but Sinneal et al. (2019) found that in one African species, plant growth and survival were significantly increased when the bacteria were present.
Circumscription of Psychotria
The pantropical tribe Psychotrieae of the Rubiaceae belongs to the subfamily Rubioideae, and includes a large proportion of the 14,000+ species of this family. The circumscription of this tribe has been narrowed in recent years to include one broadly circumscribed genus, Psychotria, and the other genera that were traditionally included here have been separated in the tribe Palicoureeae, synonymized with Psychotria (e.g., Razafmandimbison et al., 2014), or found to belong to other tribes. Also, Psychotria itself was traditionally circumscribed very broadly, to include several quite distinct lineages that have recently been separated from it. Its broad circumscription was due to its diagnosis by relatively small white flowers with valvate corolla lobes, ovules that are solitary and basal, and drupaceous fruits with generally 2 pyrenes; other genera were then separated from Psychotria based on having an unusual reproductive feature. The characters that diagnosed Psychotriea are basal in the large group of Rubiaceae to which it belongs, however, so this diagnosis made Psychotria a paraphyletic group diagnosed by plesiomorphic features of its tribe, or tribal complex.
It was recognized in the 20th century that this circumscription of Psychotria was problematic morphologically and in general too broad. This traditional broad circumscription was referred to as "Psychotria sensu lato",or "Psychotria s. lat.". Studies using molecular data (Nepokroeff et al., 1999; Andersson, 2002, Barrabé et al., 2012, Razafimandimbison et al., 2014) complemented morpholgical studies (e.g., Taylor, 1996) to distinguish lineages within Psychotria s. lat., which were separated as genera. These studies also found several Paleotropical genera nested within the Psychotria clade, which was referred to then as "Psychotria sensu stricto" or Psychotria subg. Psychotria. Genera that have now been synonymized within the new circymscription of Psychotria are from the Indian and Pacific Ocean regions and include Amaracarpus Blume, Straussia A. Gray, Psathura Comm. ex Juss., Hydnophytum Jack, and Myrmecodia Jack, Apomuria Bremek., Cremocarpon Boivin ex Baill., Grumilea Gaertn., Pyragra Bremek., and Trigonopyren Bremek. (Andersson, 2002; Razafimandimbison et al., 2014; Taylor, 2020). These studies also confirmed the synonymy of the Neotropical genus Mapouria Aubl. with Psychotria (Taylor et al., 2020), as noted by previous authors (e.g., Steyermark, 1972).
The groups that have been separated from Psychotria s. lat. in the Neotropics are now treated as Ronabea Aubl. (Lasiantheae), Coccochondra Rauschaert (incertis sedis), Carapichea Aubl. (Palicoureeae), Eumachia DC. (Palicoureeae), and Notopleura (Benth.) Bremek. (Palicoureeae). In the Neotropics, Psychotria has been circumscribed to include part (Steyermark, 1972) or all (Mueller, 1881) of the Neotropical genus Palicourea, which created confusion over the identity of Psychotria. This "traditional" Psychotria s. lat. included two main group, Psychotria subg. Psychotria and Psychotria subg. Heteropsychotria. The first group, Psychotria subg. Psychotria, corresponds to today's Psychotria or Psychotria s. str. The group Psychotria s. str. plus Eumachia corresponds to Mapouria Aubl. of Mueller (1881). The species that were included in Psychotria subg. Heteropsychotria (almost) all belong to tribe Palicoureee, and almost all of them belong to Palicourea. Confusingly, the group composed of Psychotria subg. Heteropsychotria plus Palicourea was treated as "Psychotria" by Mueller (1881). The traditionally recognized genus Cephaelis is a synonym of Palicourea, and most of its Neotropical species belong to this genus or Carapichea now.
Berger & Schinnerl (2019) and Berger et al. (2021) detailed some of the chemistry of secondary metabolites in this group, in Psychotria s. str., Palicourea s. lat., and other genera of Palicoureeae, and found chemical differences between Psychotria, which lacks alkaloids and contains tannins, and the genera of Palicoureeae, with some characteristic types of alkaloids and without tannins. They noted that the DMT of Psychotria viridis is so far the only alkaloid documented from this genus in its current circumscription, although they also noted that the genus has not been extensively sampled.
Neotropical Psychotria
Psychotria includes about 260 species in the Neotropics, which are found widely in humid and seasonal vegetation. One or more species are found in most sites, and generally a few species are sympatric in a given location. Psychotria species here are usually small to medium-sized shrubs, but range to medium-sized trees (e.g., Psychotria mexiae, Psychotria ortiziana) and also may be rhizomatous, herbaceous, understory plants (e.g., Psychotria alfaroana). The flowers are generally small (1-6 mm long), white or yellow, and pollinated by insects. These flowers generally appear to be diurnal, but a few species may be nocturnal (e.g., Psychotria ortiziana). The fruits are consistently orange or red in the Neotropical species, although the fruit color varies widely in the Paleotropics (Taylor, 2020). Most of the species are distylous across most of their ranges, but populations of some species are apparently monomorphic at least in some sites. (e.g., Sakai & Wright, 2008).
Many species of most Psychotria species characteristically dry with a gray, brown, reddish brown, or blackened color; this drying color has been cited as diagnostic for the genus, but in fact it depends at least in part on specimen preparation and perhaps plant condition and some specimens of every species have dried green. Most species of Psychotria have distinctive stipules, which are caducous and leave a line of persistent colleters or trichomes on the stem at their insertion point. These trichomes are sometimes small and only visible with a hand lens but they are characteristic when present. A few species, however, have stipules that are persistent (e.g., Psychotria grandis) or colleters that are deciduous with the stipule. Many species of Psychotria have well developed foveolate domatia; the presence and sometimes the particular form of these is often distinctive for the species. Bacterial leaf nodules are present in some Psychotria species in Africa and Madagascar, but these have not been found in any Neotropical species. A few Psychotria species have been documented to hyper-accumulate nickel when growing on nickel-rich substrates (McCartha et al., 2019); the physiological and ecological function of this is unknown, and species of other Rubiaceae genera and other families are also hyper-accumulators.
In the Neotropics, Psychotria has its centers of diversity in southern Mexico and Central America and in the Antilles. It was studied in Mexico and Central America in detail by Hamilton (1989, 1989, 1989). This genus has not been studied across the Neotropics, but a review is underway (Taylor in prep.). Most of the Neotropical species are found in wet lowland forests, but some species range into montane elevations and a few are found in seasonal vegetation and are deciduous. The general niche characteristics and consevatism of this group were studied by Sedio et al. (2013), who found that overall the Neotropical species of Psychotria are found in slightly less humid habitats than the species of Palicourea. The most widespread and commonly collected Neotropical species is Psychotria carthagenensis (Taylor et al., 2020). The Amazonian species Psychotria viridis is an enthonbotanical source of the hallucinogen DMT, and is part of the ayahuasca drug mixture and may have been transported and cultivated outside its original range. (The medicinal drug ipecac derives from a species that was formerly included in Psychotria but is now classified in a different genus, Carapichea ipecacuanha.)
Psychotria and Palicourea can be separated by several characters, including vegetative features. Psychotria generally has caducous stipules, and in the species with persistent stipules these are acute to aristate at the tip; Palicourea has persistent stipules that are bilobed at least shallowly. Specimens of Psychotria often dry dark gray or reddish brown, though not always; Palicourea specimens generally dry green, although not always and a few species consistently dry blackened. Neotropical Psychotria fruits are orange to red at maturuity; Palicourea fruits are purple-black, blue, or white at maturity, and sometimes pass through an orange immature stage but those fruits eventually do turn purple-black.
[Note: images posted by all MBG projects are included automatically here because they are identified as Psychotria sp., but are most are from Africa and Madagascar and not relevant to the taxonomic content of this page.]
Author: C.M. Taylor.
The content of this web page was last revised on 26 December 2022.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml