Poland. Flora von Schlesien. Liegnitz: Parchwitz, auf einer Wiese an der Katzbach unter den Stammarten. 10/6/99. Leg. Figert (WRSL barcode WR GS 066846; isolectotype WRSL barcode WR GS 058738) (Fig. 1).

Figure 1. 

The lectotype of Carex × ligniciensis Figert (WRSL barcode WR GS 066846). Photo: Herbarium, Museum of Natural History University of Wrocław, Poland.

The hybrid is mostly intermediate between the parental species and characterised by the following traits: ± tussocks 25–40 cm high, with numerous, shorter or longer creeping rhizomes; stems slender, with reddish brown to purple scale-like, non-reticulate basal sheaths, rough on the edges in the lower half; leaf blades 3–4 mm wide, with very long acuminate, bristle-like tip, very rough on the margin, dark green to grey-green; male spikes 1–2, oblong-cylindrical, glumes brown-black to black, obtuse, with a light central stripe, female spikes 3(–4), narrow, short cylindrical, proximate, lowermost slightly distant, lax at base, ca 4 cm long, pedunculate; female glumes ovate, shorter than utricles, dark brown; utricles empty, small, non-deciduous, green, without veins; lower bract shorter than inflorescence (Grulich et al. 2023). Wallnöfer (2006) stated that this hybrid has amphistomatic leaves (stomata on both sides of the leaves). This trait makes this hybrid impossible to confuse with the other C. buekii hybrids, which have only stomata on the lower surface of the leaves (hypostomatic). The first of the parental species, C. buekii, is hypostomatic while in the second one, C. nigra, the stomata are found on the upper (adaxial) side of the leaves (epistomatic).

This hybrid was found in floodplains of large rivers where both parental species could meet. However, C. nigra avoids warm areas with the exception of isolated lowland fen sediments in previously flooded meadows, which corresponds to all known finds of this hybrid so far.

Carex × ligniciensis is relatively rare and has been found so far in Poland, the Czech Republic and Italy (Koopman 2022). The specimens in BRNL, BRNM, CB, PR, and PRA were collected in the Czech Republic between 1921 and 1995, and they lack field verification. Therefore, we could consider it missing or even extinct at this locality. On the other hand, C. × ligniciensis is a very inconspicuous and apparently overlooked plant. In the Czech Republic, only one recent locality is known from the floodplain of the River Morava near the town of Kroměříž. As far as we know there are no recent findings of this hybrid in Poland, while its occurrence in Italy is at least questionable, as C. buekii is extremely rare in this country (Koopman et al. 2018).

The sterility of C. × ligniciensis limits it dispersal, however, the persisting of hybrid populations probably depends on vegetative reproduction, like with other sterile hybrids in Carex (Pedersen et al. 2016). The spontaneous recurrence and survival of hybrids under natural conditions are a driving force of plant speciation (e.g. Mallet 2007, Soltis 2013).

Poland. Flora von Schlesien. Liegnitz: Parchwitz, auf Wiesen an der Katzbach unter den Stammarten. 10/6/99. Leg. Figert (WRSL barcode WR GS 066847; isolectotypes: WRSL barcode WR GS 058739; JE barcode JE 00021673, barcode JE 00026167, barcode JE 00026168, barcode JE 00026169) (Fig. 2).

Figure 2. 

The lectotype of Carex × vratislaviensis Figert (WRSL barcode WR GS 066847). Photo: Herbarium, Museum of Natural History University of Wrocław, Poland.

This hybrid is very variable, often intermediate between the parental species, but also tends to be morphologically closer to one of the parents. The utricles are very different in shape and size, from small ones similar to C. buekii, to more often closer in size to C. acuta. The leaf sheaths vary with the gene flow of the parental species: from reddish brown, robust, scale-like, shiny, reticulate, to intermediate types with smaller and slender sheaths than C. buekii, dark reddish brown, in spring with distinctive reticulate sheaths and in summer without. In the field, this hybrid is striking for its vegetative traits being close to C. acuta, but it has narrow and long female spikes (longer than those of C. acuta), especially the lowest one, which is pedunculate, interrupted at the base down to individual flowers and often pendent. The lowest bract sometimes exceeds the inflorescence, a character inherited from C. acuta (Koopman et al. 2018), but it is often shorter than, or as long as, the inflorescence. Carex × vratislaviensis is usually partially or fully fertile, less often sterile. In the field, backcrosses from the hybrid swarm are fertile and their traits match the variability of either parent. These plants are morphologically indistinguishable in the field from parental species. The only distinctive trait of this hybrid is the persistent small or larger red-brown scale-like basal sheaths.

Both parental species are relatively commonly found, most often in the floodplains of large rivers, where both find suitable habitats (C. buekii: gravel-sand terraces covered with clay and littoral embankments; C. acuta: oxbows, reservoirs, eutrophic wetlands in floodplains with nutrient-rich sediments) (Kaplan et al. 2018). Most localities of C. × vratislaviensis correspond with the distribution of C. buekii, however, it was also found on banks of lakes and in adjacent marshes where C. acuta usually grows (Koopman et al. 2018). Řepka (2023) recently described large populations of the hybrid on the banks of the River Elbe near the town of Děčín (northern Bohemia), and at the edge of the field, a unique habitat completely outside the requirements of both parental species.

It has been recorded so far in Austria, Czech Republic, Germany, Hungary, Italy, Poland, and Slovakia (Koopman 2022).

Carex × vratislaviensis is an independent hybridogenous taxon (nothospecies) living autonomously in nature, mostly fully or partially fertile, and spreads spontaneously in the landscape. In the Czech Republic, it is currently documented in approximately 400 extensive populations. Based on current knowledge, it is now the most abundant hybrid (nothospecies) of the genus Carex in the Czech Republic. It has an excellent ability of clonal reproduction, and its utricles are spread by water birds to other habitats. At some habitats, especially in older meadows in the floodplains of large rivers, it can strongly dominate over the parental species or grow completely independently without their presence. In our opinion it can be compared with the hybridogenous C. recta Boott, also from the section Phacocystis, which has originated from hybridisation between C. aquatilis Wahlenb. and C. paleacea Schreb. Ex Wahlenb. (Standley 1990). It is presumed that C. × vratislaviensis influences other species and hybrids by its gene flow and forms triple hybrids or at least simply affects their fertility in situ (and the subsequent formation of empty utricles and thus empty spikes); however, this process needs further research.