Kosteletzkya borkouana Quézel, 1957

Blanchard, Orland J., 2013, A new species of Kosteletzkya (Hibisceae, Malvoideae, Malvaceae) and notes on a second species, both from eastern Democratic Republic of the Congo, Phytotaxa 88 (2), pp. 31-37 : 33-36

Kosteletzkya borkouana Quézel

A second species of Kosteletzkya from the DRC is also of note. Six years prior to the treatment of the Malvaceae in the Flore du Congo, du Rwanda et du Burundi ( Hauman 1963), a new species, Kosteletzkya borkouana Quézel (1957: 87) , was described from two specimens collected on different dates from the same locality in Tigui in the Borkou region of northern Chad, where it was said to be a rare endemic ( Quézel 1957, 1958). Unexpectedly—as this locality is some 2300 km distant in the Sahara— K. borkouana has been recognized recently as also occurring rather widely in easternmost DRC (cited as "Congo-Kinshasa") and in western Uganda and Tanzania ( Blanchard 2009). Several collections from East Africa were cited in this latter work, but precise occurrences in the DRC were not specified. Here I note the following eight Congolese collections of K. borkouana , which range through the Albertine Rift from the northern end of Lake Albert to the northern end of Lake Tanganyika:

DEMOCRATIC REPUBLIC OF THE CONGO. Mahagi Port , Lac Albert, September 1934, Brédo 1686 ( BR) ; Kasenyi , November 1935, Brédo 1880 ( BR) ; Parc National Albert , Kyavinonge (Lac Edouard), + 925 m, 20 May 1954, de Witte 10242 ( BR) ; Lac Edouard , Baie de Vitshumbi, 2 January 1953, Van der Ben 4 ( BR) ; Lac Edouard , circuit de la Rwindi, extrémité d'un bras de la baie de Vitshumbi, 19 December 1953, Van der Ben 953 ( BR) ; Kabare , bords du lac, 28 August 1914, Bequaert 5478 ( BR, US) ; plaine de la Ruzizi, 15 May 1950, Germain 6999 ( BR) ; plaine de la Ruzizi, Lac Tsimuka , 20 January 1950, Germain 5682 ( BR) .

Specimens of what is now called Kosteletzkya borkouana had actually been collected for the first time over a century ago in Uganda ("Rhino Camp," Bahr el Jebel, Lado Enclave, 10 January–2 February 1910, Mearns 2803 [ US]), but the distinctness of the species had remained unrecognized for nearly half a century until it was described in 1957 from collections made the previous year in Chad. Indeed all of the Congolese specimens cited here also pre-date the Chadian collections on which K. borkouana is based. In herbaria and in publications, these earlier Congolese collections were generally identified as K. grantii ( Masters 1868: 203) Garcke (1880: 53) or K. adoensis (Hochst. ex Richard (1847: 54) Masters (1868: 194). For example the collection Brédo 1880 cited above was listed under K. grantii in Flore du Congo, du Rwanda et du Burundi ( Hauman 1963); a study of the plant associations of the plain of the Ruzizi River identified plants of K. borkouana (see Germain 5682 and 6999 above) as K. adoensis ( Germain 1952) ; and a treatment of the flora of the Albert National Park identified the specimen Bequaert 5478, cited here, as K. adoensis ( Robyns 1948) .

Figure 3 shows the currently known distribution of K. borkouana , including the records from East Africa and Chad.

Kosteletzkya borkouana is distinguishable from K. adoensis by its erect habit, smaller flowers that are often sessile or subsessile in pairs or fascicles of three on naked peduncles, the absence of a dark spot at the petal bases, and larger fruits and seeds. From K. grantii it can be separated by its much smaller flowers, broader, more depressed, bristly capsules, and pubescent seeds. K. borkouana is found in and on the edges of marshes, often those dominated by graminoids ( Eggeling 1934, Germain 1952, Quézel 1958; Eggeling 221 [K], Lye 6989 [EA]), whereas the other two species occur in more upland habitats. Unlike either of its congeners, which are diploids, K. borkouana is a tetraploid (n = 38; Blanchard 2009, 2012).

The identification key to Kosteletzkya in the treatment of the Malvaceae in Flora of tropical East Africa ( Blanchard 2009) covers the five species that also occur in northeastern DRC (except for the new K. rotundalata ), and the use of that key will suffice to separate K. borkouana from the other species that occur there. A line-drawing illustration of a flowering specimen of K. borkouana can be found in Quézel (1958: pl. 8, fig. A).

It is now evident that the northern Chad population originated by dispersal from the Albertine Rift area or the environs, rather than the reverse. K. borkouana is an allotetraploid, and evidence from chromosome pairing in experimental hybrids indicates that the two diploid species whose genomes contributed to the inception of K. borkouana are K. adoensis and K. buettneri Gürke (1890: 92 ; Blanchard, in prep.). Both of these species occur widely in eastern DRC and western Uganda and Tanzania but they are found nowhere near northern Chad. An estimated 2.1 billion birds migrate annually between Africa and Europe ( Hahn et al. 2009), so it is not difficult to imagine an event in which a fruit or seed of K. borkouana was actively or passively picked up in the rift lakes region and deposited in Chad’s Tigui marshes during a migratory stopover. In support of this idea is the observation that the Fuirena umbellata-Epilobium mirei plant association at Tigui of which K. borkouana is a characteristic element is composed in large part of other tropical African freshwatermarsh species ( Quézel 1958: 208, 210).

Figures

FIGURE 3. Map of a part of eastern and northern Africa showing the known distributions of Kosteletzkya rotundalata (green dots, light gray in print version) and K. borkouana (red dots, dark gray in print version). Prepared by Kurt Neubig.