History of the Invasion and Distribution of Reynoutria Taxa in the Czech Republic: a Hybrid Spreading Faster Than Its Parents

Preslia, Praha, 76: 15–64, 2004 15 History of the invasion and distribution of Reynoutria taxa in the Czech Republic: a hybrid spreading faster than its parents Historie invaze a rozšíření taxonů rodu Reynoutria v České republice Bohumil M a n d á k, Petr P y š e k & Kateřina B í m o v á Institute of Botany, Academy of Sciences of the Czech Republic, CZ-252 43 Průhonice, Czech Republic, e-mail: [email protected], [email protected], [email protected] Mandák B., Pyšek P. & Bímová K. (2004): History of the invasion and distribution of Reynoutria taxa in the Czech Republic: a hybrid spreading faster than its parents. – Preslia, Praha, 76: 15–64. The distribution of four alien Reynoutria taxa (R. japonica var. japonica, R. japonica var. compacta, R. sachalinensis and R. ×bohemica), native to East Asia, and history of their introduction to and spread in the Czech Republic was studied. The most widely distributed representative of the genus, R. japonica var. japonica, was first recorded in 1883 by A. Weidmann in cultivation in S Bohemia. The first record outside cultivation is from N Bohemia in 1902. Up to 2000, it has been recorded in 1335 localities, most frequently in riparian and human-made habitats. The dwarf variety R. japonica var. compacta is of a limited distribution that depends on rare cultivation and subsequent escape. The first herbarium specimen was collected in 1948 and the first record out of cultivation is from 1995. R. sachalinensis was recorded in 261 localities. It was first collected in 1921 in Central Bohe- mia. A herbarium specimen of a plant cultivated in the Botanical Garden of the Charles University in Prague, collected in 1950, has been re-determined as R. ×bohemica, the hybrid between R. japonica var. japonica and R. sachalinensis, and represents the earliest record of the hybrid in the Czech Republic. Since then, this taxon was observed in 381 localities. Herbarium records were used to compare the rate of spread among the three common taxa in 1952–1995, i.e. since when the hybrid started to appear in herbaria. R. japonica var. japonica has been spreading significantly faster than R. sachalinensis and the hybrid exhibits twice the rate of invasion of its parents. K e y w o r d s : alien plants, Czech Republic, distribution, Fallopia, history of invasion, hybridization, habitat preferences, Polygonaceae, rate of spread, Reynoutria ×bohemica, R. japonica, R. sachalinensis Introduction Reynoutria species are native to East Asia from where they were introduced into Europe as garden ornamentals in the 19th century (Conolly 1977, Bailey & Conolly 2000). In the Czech Republic, the genus is represented by R. japonica Houtt. var. japonica, R. japonica var. compacta Moldenke, R. sachalinensis (F. Schmidt) Nakai and R. ×bohemica Chrtek et Chrtková, a hybrid between R. sachalinensis and R. japonica described from the Czech Republic (Chrtek & Chrtková 1983). All of them invade riparian and various human-made habitats and often spread into seminatural vegetation (Brabec & Pyšek 2000, Pyšek et al. 2001, 2002). Reynoutria taxa do not usually reproduce sexually within the adventive distribution area due to the lack of pollen grains in some species or inefficient seedling estab- lishment (Bailey et al. 1995). Their dispersal in the Czech Republic is therefore mainly vegetative through regeneration from rhizome and stem segments (Bímová et al. 2001, 2003, Pyšek et al. 2003). 16 Preslia 76: 15–64, 2004 R. japonica was described by Houttuyn (1777) on the basis of a herbarium specimen sent to Europe by Thunberg from Japan. R. japonica is native from North Japan through Korea and China to Taiwan (Maruta 1983, Beerling et al. 1994). The southernmost localities are in S China. The taxonomy of Reynoutria japonica in the native distribution area is not clear. For instance, Yamazaki (1994) proposed separation of Korean and Chinese populations of Reynoutria japonica on the basis of different morphology as Reynoutria forbesii (Hance) Yamazaki (ut fargesii) [syn.: R. yunnanensis (Lévl.) Nakai, R. elliptica (Koidz) Migo]. The separation of Korean and Chinese populations was followed by Yonekura & Ohashi (1997) [but within the genus Fallopia – F. forbesii (Hance) Yonekura et H. Ohashi] and confirmed on the basis of a morphological study by Kim & Park (2000). However, Yonekura & Ohashi (1997) recognized, in addition to var. japonica, two more varieties of R. japonica from Japan, i.e. var. hachidyoensis (Honda) Yonekura et H. Ohashi and var. uzenensis (Honda) Yonekura et H. Ohashi. Both are endemic to Japan and were never reported to have been introduced outside their native distribution range. Unlike in native distribution range where its morphological variation is probably high (Kim & Park 2000), the clone present in Europe is morphologically uniform and certainly results from a strong founder effect (B. Mandák et al., unpublished data). The history of early introduction of Reynoutria taxa to Europe was described in detail by Bailey & Conolly (2000). The first living plant of R. japonica was introduced in 1825 (Conolly 1977) from China and planted in Chiswick garden in Britain where it has certainly not survived (Bailey & Conolly 2000). The date 1840s reported by Bailey (1994) probably refers to the “present” clone introduced to Europe by Philipp von Siebold and quoted as Polygonum sieboldii for a long time. Since that time, Siebold’s nursery in Leiden put up for sale rhizomes of R. japonica to whole Europe. The species became pop- ular in the short term, as early as in 1847 R. japonica was awarded a gold medal by the So- ciety of Agriculture & Horticulture at Utrecht for the most interesting new ornamental plant of the year (Bailey & Conolly 2000). Introduction of a dwarf mountain variant of R. japonica referred as var. compacta,native to Mt. Fuji (Japan), relates to 1841 when the catalogue of Von Siebold & Company put on the market Polygonum pictum (an invalid synonym of Reynoutria japonica var. compacta – Bailey & Conolly 2000). In spite of early introduction, R. japonica var. compacta achieved neither popularity nor distribution of the nominate variety. However, R. japonica var. compacta was not recognized within its native distribution range, where a high morphological variation creates a continuum between R. japonica var. japonica and R. japonica var. compacta (Shiosaka & Shibata 1993). Reynoutria sachalinensis, native to Japan, Sakhalin and Ullung-do (an island between Korea and Japan), was first introduced to Europe by H. Weyrich in 1855, then by F. Schmidt in 1861 and later by C. J. Maximovicz in 1864. All plant collections from Sakhalin were delivered to St. Peterburg Botanic Garden from where they were widely distributed to European botanical gardens (Bailey & Conolly 2000). In addition, Yonekura & Ohashi (1997) recognized the taxon R. sachalinensis var. intermedia (Tatewaki) Tatewaki that is distributed in N Hokkaido, and combined it to the genus Fallopia. Neither the relation of R. sachalinensis var. intermedia to R. ×bohemica nor the degree of hybridization in the zone where R. japonica and R. sachalinensis geographically overlap has been studied. Mandák et al: History of Reynoutria invasion in the Czech Republic 17 The occurrence of R. ×bohemica, the hybrid between R. japonica and R. sachalinensis, in the area of native distribution of parental species was surprisingly confirmed quite re- cently and described as Reynoutria ×mizushimae Yokouchi by a Japanese author. How- ever, the name R. ×mizushimae does not relate to the hybrid between R. japonica var. japonica and R. sachalinensis; the former parent is R. japonica var. uzenensis Honda, combined into genus Fallopia by Yonekura & Ohashi (1997). The presence of R. ×bohemica in Japan is discussed in detail by Bailey (2003). R. ×bohemica is grown in English gardens since 1872; the oldest herbarium record co- mes from the Manchester Botanic Garden (Bailey & Conolly 2000). These authors also mention an “enigmatic” species “Polygonum Cooki” that was probably introduced from North America to Britain or raised as a product of hybridization directly in Britain. Bailey & Conolly (2000) only found a not very clear photograph from that period where Polygonum Cookii looks like R. ×bohemica or R. sachalinensis. In this case historical records are not clear enough to confirm unambiguously the identity of taxa (Bailey & Conolly 2000). The present paper is aimed at (i) describing the early history of introduction of Reynoutria taxa to the Czech Republic, (ii) presenting their current distribution in this country, and (iii) comparing the rates of their invasion. Materials and methods Study taxa Representatives of the genus Reynoutria Houtt. (syn. Fallopia Adans.) (Polygonaceae ) are herbaceous perennials with robust erect stems, an extensive system of thick rhizomes, deeply three-parted styles with fimbriate stigmas, and a functionally dioecious (gynodioecous) breeding system. There are three distinct opinions on the classification at the generic level. Some authors treat the group as a distinct genus Reynoutria (Webb 1964, Holub 1971), others as a section of the genus Fallopia, i.e. Fallopia sect. Reynoutria (Houtt.) Ronse Decr. (Ronse Decraene & Akeroyd 1988, Bailey & Stace 1992) or consider Fallopia (including Reynoutria) as a taxonomic synonym of Polygonum (Zika & Jacobsen 2003). In this paper, we follow the former approach represented by the taxonomy of Holub (1971). R. japonica var. japonica is cytologically and genetically uniform. The octoploid (2n = 8x = 88) female clone recorded in the Czech Republic (Mandák et al. 2003) belongs to the same genotype that is present in the whole Europe (B. Mandák et al., unpublished data). Since only a female clone is known in the Czech Republic, the pollen of R. japonica var. japonica is absent. Nevertheless, plants do produce seed because they are fertilized by the pollen of Fallopia aubertii (L. Henry) Holub (Bailey 2001) or R. sachalinensis (Mandák & Pyšek 1996, Mandák et al.

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