Synopsis of the genus Vitex (Lamiaceae) in the Democratic Republic of the Congo

var. rufula , V. discoideoglandulosa , V. djumaensis , V. rubroaurantiaca ). Two other taxa are subendemic, i.e. have most of their range in D.R. Congo ( Vitex congolensis var. thomasii , V. cuspidata ). Two new combinations are made ( Vitex congolensis var. thomasii , V. fischeri var. keniensis ). Nine new synonyms are proposed. A lectotype is designated for 17 names and a second-step lectotype is designated for one name. An identification key is included.


INTRODUCTION
The genus Vitex L. (Linnaeus 1753: 638 "938") comprises some 250 species almost all in tropical regions (Mabberley 2017). Until recently, Vitex was classified in Verbenaceae, subfamily Viticoideae (Briquet 1895). Harley et al. (2004) conclusively showed that Viticoideae are better placed in Lamiaceae. Very recently, subfamily Viticoideae has been restricted to three genera by new molecular phylogenetic evidence (Li et al. 2016). Vitex is the only genus of the subfamily present in Africa.
The genus Vitex awaits revision in Africa (Cabral 2013). The most comprehensive account is still Pieper's (1928) revision. Moldenke compiled much information in his "Materials towards a monograph of the genus Vitex", which has not always contributed to taxonomic clarification (Moldenke 1955a(Moldenke , 1955b(Moldenke , 1956(Moldenke , 1957(Moldenke , 1958a(Moldenke , 1958b. Vitex has recently been revised for the Flora of Tropical East Africa (FTEA) (Verdcourt 1992), and for Flora Zambesiaca (FZ) (Sales 2001(Sales , 2005. For the Democratic Republic of the Congo (D.R. Congo), the most recent account of Vitex dates back to De Wildeman (1929a). In order to prepare the treatment of the genus Vitex for the Flore d'Afrique centrale (FAC; see Sosef 2016), I have revised all the material from D.R. Congo.
During that work, a number of taxonomic and nomenclatural issues had to be solved, with implications beyond the borders of FAC, an account of which is given in the present note.
I present here a key to the species, and a check-list with a revised synonymy. When my taxonomic treatment departs from FZ and FTEA, a concise justification is provided. New combinations are coined when necessary and new synonyms are reported. Lectotypifications were necessary in a number of cases. For each taxon, a brief description is provided, focused on diagnostic traits. Detailed accounts of the taxa, including citation of specimens studied, will be published in the Flore d'Afrique centrale.

MATERIAL AND METHODS
All the relevant material from D.R. Congo in BM, BR, BRLU, COI, K, P, POZG, WAG has been examined. Additional specimens were investigated using the JSTOR Global Plants facility (http://plants.jstor.org). This material was supplemented with my own collections and field observations made in Upper Katanga between 2012 and 2016. Twentynine names have been found that are typified by specimens collected in D.R. Congo. All the specimens cited have been seen except otherwise stated (n.v.).

RESULTS AND DISCUSSION
In total, 21 taxa are recognized for the study area, i.e. 17 species, 1 subspecies, 3 varieties.
Nine new synonyms are proposed. A lectotype is designated for 17 names and a second-step lectotype for one name.
Synonymy is restricted to names that have been used in the literature for material collected in D.R. Congo. Voucher specimens are cited only for taxa that are new to D.R. Congo. Fruit colour is mentioned only if not black. Full descriptions of taxa and citation of representative material will be published in the Flore d'Afrique centrale.
Lectotypification of Vitex thonneri De Wild. The protologue cited Thonner 263, which has been widely distributed to several herbaria. Of the three sheets in BR, the one with De Wildeman's handwriting on the label is selected as the lectotype. The original material has the diagnostic characters of V. congolensis; it is unusual in having short leaflets, but this trait is variable within the species and I do not think this variant is worth taxonomic recognition.
Lectotypification of Vitex gilletii De Wild. Only one of the two syntypes has been found (Gillet 2163); the other syntype (Pogge 698) has probably been destroyed in Berlin and no duplicate could be traced. The type material of V. gilletii has leaflets with a somewhat unusual shape (low length/width ratio), abruptly contracted in a relatively long acumen. However, V. congolensis has a variable leaflet shape and size and it is impossible to discriminate taxa on that basis.  Lebrun & Stork (1997: 524). -Type: Angola, Kassambo, Büchner 574 (holo-: B †), synon. nov. Differs from the type variety by the large foliaceous elliptic lower bracts. Distribution -Subendemic to D.R. Congo, restricted to the southern margin of the distribution range of V. congolensis, i.e. Kasaï and Katanga, very locally extending to N Angola. Note -Vitex congolensis is a Guineo-Congolian linking species extremely variable as to density, length and intensity of the fulvous color of the indumentum. Variation of indumentum is continuous and cannot be translated into infraspecific units. Vitex thomasii De Wild. is a variant showing a very unusual character, i.e. foliaceous bracts at the lower inflorescence nodes, up to 30 × 8 mm. This is not a teratological condition, because several gatherings from distant localities exhibit such bracts. This variant deserves taxonomic recognition at varietal rank. The type specimen of V. buchneri has not been found. However, the protologue clearly indicates that this taxon belongs here ("…die Bracteen der Nebenachsen erster Ordnung lanzettlich in den Stiel verschmälert, mit dem Stiel bis 3 cm lang…") (Gürke 1893). Hiern (Hiern 1900: 835); Baker (1900: 521); De Wildeman (1912a: 467;1929a: 9); Pieper (1928: 70); Moldenke (1955b: 307; Wildeman 1914a: 141;1914c: 405;1921: 164); Pieper (1928: 40, 60 & 83); Moldenke (1956: 420); Lebrun & Stork (1997: 524 Notes -Vitex cuspidata Hiern is known from very few collections mostly from Angola, all of them in fruit (Cabral 2013). Pubescence of ovary is unknown and, accordingly, the species keys out in two groups in the key. Material from the Sudanian region has also been ascribed to that taxon (Aubréville 1950: 500) but it is certainly not conspecific. The type material of Vitex kapirensis is a good match of the type material of Vitex cuspidata, with a large inflorescence, relatively small fruits, long-petiolulate elliptic leaflets contracted into a short acumen. V. kapirensis was synonymized  with V. fischeri, but the latter has much larger leaflets and tertiary veins forming a more conspicuous ladder pattern.

Vitex cuspidata
Lectotypification of Vitex kapirensis De Wild. The type material of Vitex kapirensis consist of four sheets; the sheet with the most complete material and the most extensive collecting information is selected as the lectotype.  A small tree. Leaves in whorls of 3. Leaf glabrous except for ciliate domatia; leaflets 5; petiolules 3-17 mm; lamina coriaceous, acute or shortly acuminate. Inflorescence of dichasia; peduncle short (< 2 cm), calyx 2 mm, ovary hairy. Fruit small c. 9 × 7 mm.

Vitex madiensis
A small tree. Leaves 1-3-foliolate; leaflets coarsely crenate-dentate, smooth above, the middle one long petiolulate. Inflorescence of dichasia, long pedunculate, pedicels with long whitish fine hairs; calyx 2-3 mm, broadly campanulate, broad triangular teeth 0.5-1 mm, with long whitish hairs; corolla whitish-mauve 6-8 mm, stamens included; ovary glabrous. Lectotypification of Vitex camporum Büttn. Vitex cam porum is based on three syntypes which have all been destroyed in Berlin (Büttner 427 & 428;Welwitsch 5728). Two duplicates of Welwitsch 5728 have been found in BM, and one duplicate of Büttner 427 has been found in K (K barcode K001008451); all the duplicates match the description in the protologue. Welwitsch 5728 is a better specimen and one of the two sheets is thus selected as the lectotype.
Lectotypification of Vitex camporum var. longipedi cellata De Wild. De Wildeman cites one collection from Kwamouth by E. & M. Laurent, s.n., which corresponds to two sheets in BR. The sheet with collecting data on the label is chosen as the lectotype.
Lectotypification of Vitex schweinfurthii Gürke. The protologue cites two collections i.e. Schweinfurth 2030 & 2848. These specimens have been destroyed in Berlin. A duplicate of Schweinfurth 2030 matching the description in the protologue exists in K, and is here selected as the lectotype.
Differs from the type subspecies by the following traits. A shrub. Twigs stout, often wine red. Leaves 5 foliolate; lamina abruptly contracted at tip and cuspidate, very coriaceous, entire; upper surface very scabrid, reticulum prominulent. Distribution -Zambezian region, from Angola eastwards to Tanzania and Mozambique. Notes -Dwarf, geofrutescent forms of V. madiensis subsp. milanjiensis occur throughout the distribution range of subsp. milanjiensis. They have been repeatedly described as V. hockii De Wild., V. ringoetii De Wild., V. epidictyodes W.Piep., V. caespitosa Exell. Such forms pose two different taxonomic problems. First, it is unclear if they are genetically fixed or if, alternatively, they represent pyrophytic forms induced by burning; Verdcourt (1992) favoured the former hypothesis. Secondly, assuming it is genetically fixed, it is not clear if that morph is monophyletic or, alternatively, if it has evolved several times independently in response to selection by fire or other environmental constraints. I have not been able to find differences between dwarf and tall morphs except size.
Lectotypification of Vitex epidictyodes Mildbr. ex W.Piep. Three syntypes are cited in the protologue (Stolz 556; Stolz 1478; Trotha 95). Pieper (1929) designated Stolz 556 as the lectotype (see Verdcourt 1992). Many specimens of that gathering have been distributed and Pieper (1929) did not indicate a specific herbarium; therefore second-step lectotypification is necessary (art 9.17 of ICN;McNeill et al. 2012). Since Pieper worked in Berlin, I therefore select the specimen kept in Berlin as the lectotype.
Both match the protologue. The latter is a better preserved specimen and is therefore chosen as the lectotype.