Identification of Pennisetum cultivars available in trade in Europe
A number of Pennisetum cultivars are traded in the EPPO region, including Cherry Sparkler, Fireworks, Rubrum, Sky Rocket, and Summer Samba. There has been a debate to whether these cultivars belong to a separate species, Pennisetum advena (only known from cultivation), or to the broader species concept: Pennisetum setaceum, or they are cultivars of a hybrid (derived from P. setaceum and P. macrostachyon). This discussion has a renewed interest with the inclusion of P. setaceum on the EU List of Union concern (Regulation 1143/2014), where the species, and all its lower taxa or hybrids are subject to the same prohibitions (e.g. ban from sale). Provisional molecular research indicating that these cultivars are distinct from P. setaceum, has led to them being currently excluded from listing. An additional study was conducted where live Pennisetum species and the above-named cultivars were collected from trade. Additionally, over 160 herbarium specimens belonging to 10 Pennisetum species were examined for the study. Naturalized P. setaceum plants were collected from the Canary Islands and Catalonia, Spain. Ornamental P. setaceum were collected in New Zealand. A morphological and molecular comparison of all material showed that all cultivars that are currently in trade in Western Europe belong to a separate species P. advena. Distinct differences were shown in morphological comparisons (e.g. inflorescence, width of the leaf blade, the leaf blade being flat or involute, the central vein being swollen or not, and the length of the stipe) and molecular comparisons (the chloroplast markers rbcL and trnH-psbA, differ in 2 and 4 base pairs, respectively, and there is only a 90% overlap of the nuclear ITS sequence between the two species). These results further justify the exclusion of the above named Pennisetum cultivars from the EU List of Union concern.
Sources
Van Valkenburg JLCH, Costerus M, Westenberg M (2021) Pennisetum setaceum or Pennisetum advena cultivars, what ornamental do we have in our garden. Ecology and Evolution 11(6), 11216-11222. https://doi.org/10.1002/ece3.7908