Cremocarpon

Taylor, Charlotte M., 2020, Overview of Psychotria in Madagascar (Rubiaceae, Psychotrieae), and of Bremekamp’s foundational study of this group, Candollea 75 (1), pp. 51-70 : 61

Cremocarpon and Pyragra

Bremekamp’s Cremocarpon and Pyragra

BREMEKAMP (1958, 1963) re-characterized and expanded the poorly known genus Cremocarpon , and described Pyragra with several similar features. These were both separated from Psychotria by their unusual fruits, which are schizocarpous with two mericarps that are connected to a fibrous carpophore ( Fig. 5). Cremocarpon was further diagnosed by its ellipsoid fruits with hemispherical mericarps ( Fig. 5A–M), and Pyragra by its laterally compressed fruits with mericarps that are flattened and winged ( Fig. 5N–Q). BREMEKAMP (1958) included in Cremocarpon eight species from Madagascar, one from the Comores ( C. boivinianum Baill. , the type of the genus), and one from New Caledonia ( C. rupicola ), and considered this last species to represent a striking biogeographic disjunction in this group. The species of Pyragra are similar to each other and grow in the same region in Madagascar. These two genera were provisionally synonymized with Psychotria by SCHATZ (2001), but were recognized by other authors ( PIESSCHAERT, 2001; DAVIS et al., 2007).

The dehiscent schizocarpous fruits of these genera are highly unusual morphologically in Psychotrieae , and their form and origin are of interest for understanding this tribe. This unusual fruit form is studied in detail below for this reason, both morphologically and as to results of molecular systematic analysis. The unusual fruit form of these two genera is apparently not otherwise known in Psychotrieae , but not entirely unlike that of other species. The mericarps of Cremocarpon ( Fig. 5A, C–D, H, J) resemble the pyrenes of fleshy-fruited Psychotria species, and the distinctive flattened mericarps of Pyragra ( Fig. 5N, Q) are similar to the flattened, laterally winged pyrenes in the fleshy fruits of some Pacific Psychotria e.g., P. ireneae Barrabé (BARRABÉ, 2014: 107, fig. 4), P. eumorphanthus Fosberg ( PIESSCHAERT, 2001: 407, fig. 10.7A–C). And, the carpophores of the schizocarpous fruits agree in position and form with fibrous structures that are generally found inside the fleshy fruits of Psychotrieae and Palicourea ( CAPURON, 1973; PIESSCHAERT, 2001). Thus, it seems likely that the fruits of Cremocarpon and Pyragra differ their dry and dehiscent mature condition, not in their basic anatomy or form, so it is not unlikely that this feature has been derived more than once in Psychotria ( CAPURON, 1973) . Beyond this, the endosperm form of the various Malagasy species of these two genera vary widely, as detailed by BREMEKAMP (1958). The form of the carpophores and mericarps also varies among the species of these genera, and the fruits may vary in mode and perhaps even presence of dehiscence. The two Pyragra species ( Fig. 5N–Q) have ovoid, apparently dry mericarps with flattened margins, and are borne on a well developed, flattened carpophore that is formed by (or next to) the septum and persists on the pedicel, and the mericarps apparently fall separately. The fruits of C. lantzii are similar to those of Pyragra except its mericarps are smaller and ellipsoid, and appear to separate or fall off simultaneously from the persistent carpophore. The fruits of C. boivinanum ( Fig. 5A), C. fissicorne Bremek. , C. pulchristipulum Bremek. , C. sessilifolium Bremek. , and C. tenuifolium Bremek. have slender carpophores that are bifid at the top, and unwinged mericarps that separate from each other but remain attached to the carpophore at the top. And, PIESSCHAERT (2001: 326) did not find clearly developed schizocarpy in the New Caledonia species of Cremocarpon , and suggested that its fruits are not schizocarpous but just contain well developed mesocarp fibers that persist on the pedicels after the rest of the fruit has fallen. Such fruit fibers are particularly well developed in the Malagasy species C. trichanthum ( Fig. 5I–M), and clearly developed schizocarpy has similarly not been found in this species in this current study; in fact, its fruits are white at maturity and become juicy inside a stiff or leathery exocarp that covers the entire structure. Thus, based on morphological study, the schizocarpous fruits of Cremocarpon and Pyragra do not all share the same form but are actually heterogenous, so they probably do not share a single evolutionary origin, and some of these fruit structures appear to be misinterpreted. This means that even though this fruit character is unusual and distinctive, it is problematic as the diagnostic character of a genus.

Bremekamp’s Cremocarpon and Pyragra analyzed with molecular data

ANDERSSON (2002) included two species of Cremocarpon in his analysis, the New Caledonian species and the Malagasy C. lantzii , and no species of Pyragra . He found the Cremocarpon specimens nested within Psychotria , and synonymized these based on his analysis. He also synonymized Pyragra based on PIESSCHAERT’s (2001) suggestion that this might be justified. RAZAFIMANDIMBISON et al. (2014) analyzed 11 identified samples of these genera, with the two species of Pyragra and eight samples of Cremocarpon : seven from Madagascar, representing six species and one unidentified sample, and the New Caledonian species. They also analyzed the systematic distribution of schizocarpous fruits in Psychotrieae . Razafimandimbison et al. found Cremocarpon and Pyragra nested in Psychotria , and synonymized these genera. They found at least two independent occurrences of schizocarpous fruits in Psychotria , with the New Caledonian species placed on a different regional clade from the schizocarpous Malagasy and Comoran species. The schizocarpous species were placed basally in their Western Indian Ocean clade, with the C. lantzii separated from the other schizocarpous Malagasy and Comoran species. Razafimandimbison et al. posited that schizocarpous fruits evolved once among the Psychotria species in this region, and suggested that this entire Psychotria clade may ancestrally have had schizocarpous fruits and then had one subsequent reversal to the drupaceous fruits found in most of the species.