The 'minor confusion' around Parquetina nigrescens (Periplocaceae)

A correction of the taxonomy of Parquetina nigrescens (AIz.) Bullock with its synonyms Periploca nigrescens Alz. and OmphaJogonus calophyllus Bail!. is presented. Our investigation reveals that Perip/oca nigrescens and Omphalogonus calophylfus are two distinct taxa, as their floral morphology differs conspicuously. The name, Parquefina nigrescens, is therefore an incorrect combination. A taxonomic revision of Periploca nigrescens and Omphalogonus calophyllus completes this account.

Bull ock in 1961 combined Periploea lIigrescens, Pa rquetina gabonicQ and Omphalogonus calophyllus as Parquetina nigrescens (Af?.) BUllock. It is unclear how Bu ll ock cou ld have come to this conclusion on evidence from the Oond morphology of the two taxa. O ur o wn invcstigation revealed majo r di ffcrences between the flowers of Periploca nigrescens and Omphalogonus calophyllus. Periploca nigrescens has the typic al rotale Periploca flower w ith indistin ct shallow corolla tube and exserted gynostegium. Omphalogonus calophylills, in contrast , has flowers with a well-developed campa nulate corolla lube, within which the gynostegium is enclosed .
Periploca nigresccns and Ompha[ogonlls calophylllls be lo ng to two di stinct groups of taxa in the Periplocaccae. The first group's fl owers are rotate. having shallow, sa ucer-shaped coro lla tubes from which tbe gynostcgia are exsertcd. The second group has. flowers with distinct campan ul att.! to tuhular corolla tu bes wi th in which the gynostegia an~ encl osed . Peril'ioca Iligrescens accordingly helongs tn the first group and Ol1lphaiogonlls cafophylllts to the second grou p.
Instead of cle aring up a 'min or confusion' Bull ock ( 1961) created a major confusion. An important fac tor that probably, at least partly, led to Bullock's co nfusion, is the conspicuously similar vegetative appearance of the two species and the fact that ho th species' twi gs, leaves, peduncles and flowers arc hlack when dry. Their leaves are so similar in sbape, texture and appearance that it is d ifficult. sometimes imposs ible, to Id entify sterile mate rial with total certainty to any one of the two species.
N .E.Brown (11)02) was mos t definitely correct in his recognition of Parquetina gabonica a.I; Periploca nigrescens and in his maintai ni ng OmpiJaiogonus caiophyllus as a disti nct taxon. Bu llock's (1961) allegation that N .E. Brown (1902) was at fault is therefore unfounded , Bullock's 'evidence of sexual dimorphy' is possib ly the result of co nfus ion caused by Ihe large conspicuous anthers of Peripioca nigrescens and the small, 1css·conspicuous an thers of Ompitalogolllls calophyLllls .

Material and Methods
Herbarium specimens from the herbaria of HM , BR , COl, K. L, LISe, MO, p, PRE, SRGH and WAG were studied . Ex ternal morphology was examined wi th an Olympu s stcreo·microseope. Pollen was co llected fr om the above-mentioned specimens and acetolysed according to tbe method of Erdtman ( 1960), mounted in glycerme jdly and sealed with paraffin wax. Samples were examined with a Zeiss microscope (LM). Measurements of tetrad size were , whenever possible, based on a minimum of 15 tetrads per specImen. For the scanning electron microscope (SEM), pollen was acetolysed , mrdried on stubs, coated with gold and exam ined . A Jeol Winsam 6400 electron microscope was used.

Account Pollen morphology
Omphalogonus calophyLlus: Its pollen grains arc united in tetrads with these grains arranged decussately and only a small proportio n rhomboidall y (Figure 1 a & b). The decussate tetrads are (31.5-40.5) 35.9 x 34.7 (27.9-39.6) mm. Three to four pores occu r per grain, the pore size being 0.7-2 .2 mm . These pores are sometimes covered by a tbin layer of exine material. The exine is smooth.
Periploca nigrescens: The pollen grains of this species are united in tetrads with these grains arranged rhombo id ally or deeussate ly (Figure 2a-<1). Both types are commo n. The rhombo idal tetrads me.,ure (59.4-93.6) 72 .7 x 63 (49.5-H5.5) Illm. The dc-cussatc tetrad size amoun ts to (58.5-H7.3) 67.7 x 62.X (46.8-84.6 ) mm. Four to six pores occur per grain, the size of the pores being 2.2-5.1 mm. The pores are sometimes covered by a thin layer of exine material. The exine is smooth. The poll e n of Periploca Iligrescells is similar to tha t found in the other species of Peripioca, although its grains are large r than in most of (h e species (Verhoeven & Venter 1994).

Specimens examined
Uses: P nigrescens is used as an tidote against wonns. It s late x is used for ski n troubles.
Distribution and ecology: This species is dis tributed from Sierra Leone and Guinea in lhe west, eastwards to the eastern border of Zaire (Figure 6). Although a La rge coll ecti on of herbarium specimens exist of P nigrescens, little can be learn t about this spec ies' ecology and habitat from the speci men labels. It has been coll ected in maritime thic ke ts, on ant hi lls and in gallery forest, where the species may be commo n. When considerin g the distribution pattern of P nigrescens through tropical Africa the deduc tion can bc made that it is a member of tropical forest and savannah .