2. Reynoutria compacta (Hook.f.) Nakai (syn.: R. japonica var. compacta (Hook.f.) Buccheim, Fallopia japonica var. compacta (Hook.f.) J.P. Bailey, F. compacta (Hook.f.) G.H. Loos et P. Keil, Polygonum compactum Hook.f.) (Japan, Korea) – A very rare garden throw-out, escape from or relic of cultivation. Known since 1981 from rather few places. Perhaps best known (and still present) from Antwerpen-Linkeroever, doubtlessly as a mere relic. Furthermore seen in 2010 in Balen (Keiheuvel) and Lanaken-Neerharen (Hochter Bampd).
The taxonomic status of Reynoutria compacta has long been uncertain. Loos (2010), mainly summarising previous studies, strongly recommended specific status. Molecular research by Galasso & al. (2009) confirmed its distinctness. In fact, it proved to be more closely related to Reynoutria sachalinensis than to R. japonica. It is also morphologically, chorologically and ecologically rather different. From Reynoutria japonica it is easily distinguished by its dwarf habit (not exceeding 100 cm and often only 30 cm high), smaller, thicker leaves, often with undulate margins, pinkish-reddish tepals, etc.
Selected literature:
Conolly A.P. (1977) The distribution and history in the British Isles of some alien species of Polygonum and Reynoutria. Watsonia 11: 291-311.
Galasso G., Banfi E., De Mattia F., Grassi F., Sgorbati S. & Labra M. (2009) Molecular phylogeny of Polygonum L. s.l. (Polygonoideae, Polygonaceae), focusing on European taxa: preliminary results and systematic considerations based on rbcL plastidial sequence data. Atti Soc. It. Sci. Nat. Museo Civ. Stor. Nat. Milano 150(1): 113-148.
Loos G.H. (2010) Taxonomische Neukombinationen zur Flora Mittel- und Osteuropas, insbesondere Nordrhein-Westfalens. Online-Veröff. Bochumer Bot. Ver. 2(1): 1-20.