Mapouria guianensis Aubl., Hist. Pl. Guian. 1: 175. pl. 67. 1775., not Psychotria guianensis Raeusch. Nomencl. ed. 3. 56. 1797, nor Psychotria guianensis (Aubl.) Rusby, Mem. Torrey Club 3: 48. 1893 = Palicourea guianensis Aubl. 1775.
Psychotria nitida Willd., Sp. Pl. 1: 963. 1798, superfluous name.
Psychotria mapuria R. & S., Syst. Veg. 5: 187. 1819, superfluous name.
Psychotria trinitensis Urb., Symb. Ant. 7: 441. 1913.
The proper epithet for this taxon poses nomenclatural problems. Although the binomial Psychotria guianensis Raeusch. appears in Raeuschel’s Nomencl. Bot. ed. 3, 56. 1797, most botanists consulted agree that this is a nomen nudum without either a direct or indirect reference to any previously published name, and therefore illegitimate. Both Kew Index (1895) and Bremekamp (Rubiaceae, Flora Suriname, p. 215. 1934) supposed that Psychotria guianensis Raeusch. was based on Palicourea guianensis Aubl. Bremekamp used the combination Psychotria guianensis (Aubl.) Raeusch. under Palicourea guianensis, but indicated (in letter) that the name should have been quoted as Psychotria guianensis (Aubl.) Raeusch. ex Steud., since Steudel published the combination in his Nomencl. 582. 1821. Rusby (Mem. Torrey Club 3: 48. 1893), on the other hand, made the combination Psychotria guianensis (Aubl.) Rusby on the basis of Palicourea guianensis Aubl.
The view, however, that Psychotria guianensis Raeusch. is based on Palicourea guianensis Aubl, is not shared by some botanists, who believe instead that Raeuschel’s name is based on Mapouria guianensis Aubl. To follow this reasoning through, it should be noted that Raeuschel in his delimitation of genera followed Schreber (Linnaeus, Gen. Pl. ed. 8. 1789). This is an important point, since Stephanium of Schreber (Linnaeus, Gen. Pl. ed. 8. 1: 124. 1789) is congeneric with Palicourea of Aublet, and we find Stephanium guianense taken up by Raeuschel as no. 387 in his Nom. Bot. ed. 3. 55. 1797, is to be interpreted as S. guianense (Aubl.) Raeusch. According to this interpretation, Psychotria guianensis of Raeuschel’s Nom. Bot. ed. 3. 56. 1797 refers to a different taxon, namely Mapouria guianensis Aubl. As Swartz (Obs. Bot. 75. 1791) had united Mapouria Aublet with Psychotria, it is reasoned that Raeuschel adopted Mapouria guianensis Aubl. and placed it under Psychotria as a new combination in his Nom. Bot. ed. 3. 56. 1797, as Psychotria guianensis (Aubl.) Raeusch. Whether one is justified in upholding such a combination as legally published is debatable, however.
Since the application of Raeuschel’s Psychotria guianensis could be interpreted differently by various authors, its use as a legitimate name is open to question, and it would seem better treated as a nomen nudum in the more usual interpretation of this concept. Hence, it is necessary to find the next legitimate name available for the taxon of Mapouria guianensis when transferred to Psychotria. The next two names available, Psychotria nitida Willd. (1798) and Psychotria mapuria Roem. & Schult. (1819), are both illegitimate as superfluous names, as each of these authors cited Mapouria guianensis Aubl. in synonymy, instead of transferring Aublet’s Mapouria guianensis to Psychotria.
We are left, then, with the next available epithet. This is Psychotria mapourioides de Candolle, published in 1830. It was collected by Patris in British Guiana. A photo of the type from the Delessert Herbarium shows the fruiting axis with four lateral basal axes, as is the same encountered also in the type specimen of Mapouria guianensis. Other features of Psychotria mapourioides, which can be observed on the type photo, are the 7-8 lateral nerves on each side of the midrib, obovate-elliptic, subobtuse or obtuse leaves acuminate at the base and 16.5 × 7 cm, an obovate stipule rounded at the apex and 2-2.2 × 1.5 cm, peduncle 7-8 cm long, infructescence 5-6 cm high by 8-8.5 cm broad with the axes in two tiers, four at the base and four above, with the lowest axes measuring 2.7 cm long.
Although de Candolle stated that his plant was collected in British Guiana, the label on the photo of the type specimen indicates “Cayenne.” Nevertheless, this type of plant is well matched by many collections from both British and French Guiana, and is the plant commonly passing in herbaria as Psychotria trinitensis Urb. and Psychotria mapouria R. & S., having the four lateral basal axes of the inflorescence supported by an elongated peduncle.
Bremekamp (Rubiaceae, Fl. Surin. p. 228. 1934) placed Psychotria mapourioides DC. as a synonym under Mapouria chionantha, but de Candolle’s name is the first one used in Psychotria proper and is the name that can be related directly to the common plant of British and French Guiana with four basal lateral axes to the inflorescence, as well as relating to the specimen of the type of Mapouria guianensis Aubl. Moreover, usually only two lateral basal axes are present on most specimens of Psychotria chionantha, as judged by the type specimen and by other specimens collected near the type locality of Psychotria chionantha. The relatively few lateral nerves (7-8) shown on the type photo of Psychotria mapourioides do not agree with the more numerous number (10-15) found on the type specimen of Palicourea chionantha DC. from Bahia nor as described by Bremekamp under Mapouria chionantha with “nerves 10-12 on each side.” Thus, Bremekamp’s reduction to synonymy of Psychotria mapourioides under Mapouria chionantha is incorrect insofar as the number of lateral nerves is concerned.
The various taxa in this group have been maintained by Bremekamp as distinct species, i e Mapouria chionantha and M. opaca. After an intensive study in an attempt to segregate these taxa, it has been concluded that there is too much variation and intergradation to maintain the taxa in a specific category. The relative degree of prominence and number of the lateral nerves of the leaf blades, leaf shape, degree of pubescence of the corolla exterior, pubescence of peduncle and inflorescence, and size of leaf—all these characters show too much variability.
It appears, therefore, more in keeping with the natural variation within this group to place all the variations under Psychotria mapourioides DC., the earliest valid name for the group. Those specimens of P. mapourioides having the lowest lateral axes in three’s or four’s are regarded as typical and agree with P. mapourioides and Mapouria guianensis Aubl., whereas those specimens with only two basal axes commonly present agree with the type encountered commonly in P. chionantha and P. opaca. Moreover, the specimens having broad leaves prominently nerved are taken as the ones agreeing best with Mapouria guianensis and typical P. mapourioides, whereas those with the leaves less prominently nerved and narrower are placed with P. chionantha and P. opaca. Furthermore, the dorsal spur-like thickening at the apex of the corolla lobes is not a reliable character, and may be present or lacking on both typical P. mapourioides, Mapouria guianensis, and P. chionantha.