Taxonomy and nomenclature

Paspalum thunbergii Kunth, Révis. Gramin.: 25. 1829 ≡ Paspalum scrobiculatum var. thunbergii (Kunth) Makino in Bot. Mag. (Tokyo) 10: 60. 1896. — Fig. 1 & 2.

= Paspalum dissectum Murray, Syst. Veg., ed. 14: 104. May–Jun 1784, nom. illeg. [non Paspalum dissectum (L.) L., Sp. Pl., ed. 2, 1: 81. 1762],

— Paspalum dissectum sensu Thunb., Fl. Jap.: 45. Aug 1784 [misapplication of P. dissectum (L.) L. 1762].

Description (adapted from Chen & Phillips 2006) — Perennial from short, knotty rootstock. Culms tufted, erect, 50–100 cm tall; nodes glabrous (or pilose). Leaf sheath keeled, hirsute; leaf blade linear, 10-25 × 0.5-0.8 cm, hirsute on both surfaces, rarely glabrous, apex acuminate; ligule membranous, 0.5–1.5 mm long, apex truncate. Inflorescence axis 1-9(-12) cm long; racemes (2 or)3-6, laxly ascending or spreading, 3–9 cm long, axils pilose; rachis 1–1.5 mm wide, margins scaberulous; spikelets commonly paired, at least in central part of raceme (or a vestigial 2^nd spikelet present); pedicels minutely puberulous. Spikelets elliptic to orbicular-elliptic, plumply planoconvex, 2.5-3 × 2-2.3 mm, apex rounded or subacute; lower glume absent, rarely vestigial; upper glume membranous, sparsely pubescent especially along margins, 3-veined with lateral veins marginal; lower lemma similar to upper glume but glabrous; upper lemma pallid, as long as spikelet, coriaceous, punctulate-striate, apex obtuse.

Remarks — Linnaeus (1762) recombined Panicum dissectum L. as Paspalum dissectum (L.) L., giving the provenance as “in America calidiore”. Murray (May–Jun 1784) gave no provenance for Paspalum dissectum Murray and made no reference to Linnaeus or Thunberg (as he did, e.g., under the preceding species, Phalaris hispida Thunb.); he therefore published an illegitimate later homonym. Thunberg (Aug 1784) misapplied the name P. dissectum (L.) L. to a Japanese plant, citing Linnaeus (1762) and using exactly the same diagnostic phrase name as did Murray. Kunth (1829) adopted the name P. thunbergii Kunth for the species to which Thunberg misapplied P. dissectum, citing “P. dissectum Thunb. Jap.” (i.e. Thunberg 1784) in synonymy, not mentioning P. dissectum Murray, and giving the provenance as “Japonia, Java”; he clearly excluded the correctly applied P. dissectum (L.) L. because he accepted that species separately (l.c., as “P. dissectum Linn. Sp.” from “America calid., Brasilia”). Kunth included no description or diagnosis in the protologue of P. thunbergii, but the name was validly published by the reference he provided to the diagnosis in Thunberg (1784). Steudel (1853: 28) published P. thunbergii, ascribing the name to Kunth and providing a diagnosis, citing “P. dissectum Thunb. Jap. 45. non Lin.” This is clearly a subsequent use of the already validly published P. thunbergii Kunth, not a new name attributable to “Kunth ex Steud.”

The systematic position of Paspalum thunbergii is uncertain and, to our knowledge, this species has not been included in molecular phylogenetic studies. It is similar to P. scrobiculatum L. and has been combined under that species, as P. scrobiculatum var. thunbergii (Kunth) Makino (Makino 1896). This and related species have been accommodated in the informal Plicatula Group, which is characterized by usually dark brown upper lemmas (e.g. Rua & al. 2009), which are pale in P. thunbergii. Cidade & al. (2013) referred to this group as a highly complex assemblage.

From its putative relatives, Paspalum plicatulum Michx. and P. scrobiculatum, both with a more or less pantropical distribution, P. thunbergii is distinguished by upper lemmas that are pale at maturity. With the similar P. longifolium Roxb. — also widespread and weedy — it shares the pale upper lemmas, but this species has more numerous racemes (up to 20), smaller spikelets (2–2.5 mm long), and a broader rachis up to 4 mm wide.

Compared with the species of Paspalum hitherto known to occur in Italy, P. thunbergii is most similar to P. dilatatum. Both are tufted, fairly robust perennials with racemose inflorescences with 2–6 spreading branches and paired spikelets. However, in P. thunbergii the leaf blades and sheaths are densely hirsute hairy, spikelets are slightly smaller (2.5–3 mm long, vs 2.8–4 mm long), rounded to subacute at the apex and only sparsely and very shortly pubescent, especially along the margins (vs acuminate at the apex, with long-ciliate margins). Moreover, P. thunbergii typically has upper glumes that are 3-veined with a very prominent central vein and marginal lateral veins (vs 5-7-veined upper glumes in P. dilatatum). Also, both species are ecologically rather different (see below). Paspalum thunbergii and P. dilatatum locally have likely been confused in Italy or elsewhere in Europe. However, a revision of herbarium specimens of the latter in some herbaria (BER, BR, HBBS, GENT, MSNM, PAV and TO; acronyms according to Thiers [continuously updated]) only yielded one supplementary record of P. thunbergii (see specimens examined).

Fig. 1.

Paspalum thunbergii in Italy. — A: forest path in Boscaccio: B: roadside ditch in Mortara; C: rhizome; D: inflorescence; E: spikelets. — A: Boscaccio, photographed in August 2015 by Guido Brusa; B–E: Mortara, photographed in August 2015 by Nicola Ardenghi.

Fig. 2.

Paspalum thunbergii: A: general habit; B: leaf sheath; C: spikelet abaxial surface; D: spikelet adaxial surface. — Paspalum dilatatum: E: spikelet abaxial surface; F: spikelet adaxial surface. — Drawn by Antonio Fernandez; A–D from [see selected specimens examined] G. Brusa s.n. (BR); E, F from France, Landes, Ondres, N of Bayonne, alongside Etang d'Irieu, 19 Jul 1979, J. E. De Langhe 424/79 (BR).

Ecology and habitat preferences

In its area of origin (see below) Paspalum thunbergii occurs in fields and waste places, usually on moist soils (Chen & Phillips 2006). In Boscaccio, P. thunbergii grows alongside a forest path over a distance of c. 180 m. The species mostly occurs on the edges of the path, not in the centre where trampling seems to prevent its development. As a consequence, the plants of P. thunbergii grow in interrupted linear stands 50–100 cm wide; a total area of about 70 square meters is currently occupied by the species at this site. The flowering period starts in the middle of August and continues until the first frost (mostly at the end of October or later). Seedlings were not recorded in the surroundings of the flowering plants; spreading seems to be mostly (or entirely?) vegetative, i.e. by means of the short rhizomes. However, new stands are likely to establish from seed. The soil is mainly loamy and water stagnation occurs after abundant rainfall. At the end of summer, hygrophilous species grow together with P. thunbergii, such as Carex sylvatica Huds., Lycopus europaeus L., Lythrum salicaria L. and Persicaria hydropiper (L.) Spach; the protected Eleocharis carniolica W. D. J. Koch (Annex II, Habitats Directive 92/43 of the European Union) was also recorded in a small pool nearby. However, weedy species are most frequent: Echinochloa crus-galli (L.) P. Beauv., Plantago major L., Poa annua L., etc., especially short-lived alien species such as Bidens frondosa L., Digitaria violascens Link, Erigeron annuus (L.) Desf. and Panicum dichotomiflorum Michx. and perennial aliens such as Juncus tenuis Willd., Muhlenbergia schreberi J. F. Gmel., Oxalis stricta L., Potentilla indica (Jacks.) Th. Wolf and Solidago gigantea Aiton. Paspalum thunbergii does not exhibit the ability to invade the nearby heathland, where a monospecific stand of Molinia arundinacea Schrank covers the understory.

The population of Paspalum thunbergii in Mortara occupies a linear area of about 260 × 1 m between an unsurfaced road and a rice field channel with a cover ranging from about 80% (at the border of the population) to 95% (most of the area); other species have a <1% cover [e.g. Convolvulus arvensis L., Linaria vulgaris Mill., Potentilla reptans L., Ranunculus acris L., Setaria pumila (Poir.) Roem. & Schult., Sorghum halepense (L.) Pers., Trifolium repens L., Urtica dioica L., Vicia cracca L.]. Paspalum thunbergii usually avoids the channel bank, which is occupied by a well-developed Magnocaricion elatae community (Carex acutiformis Ehrh., Convolvulus sepium L., Lotus pedunculatus Cav., Lythrum salicaria L., Solanum dulcamara L., Sparganium erectum L., Symphytum officinale L., Urtica dioica L.). With its greenishbluish erect leaf blades, the plants are visible from a distance. In Mortara, the species surely spreads both by seed and vegetatively.

Distribution and weed status in the world and in Italy

Paspalum thunbergii is originally native in E Asia. It is widely distributed in India (Darjeeling, Sikkim), Bhutan, China (provinces of Anhui, Fujian, Guangdong, Guangxi, Guizhou, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shandong, Sichuan, Yunnan and Zhejiang), Taiwan, Korea and Japan (Chen & Phillips 2006). It is known as an introduction further to the west. Tsvelev (1984) reported it from the former Soviet Union in Georgia and Azerbaijan and, more recently, it was discovered in NE Turkey (e.g. Terzioğlu & Anşin 2001; Korkmaz & al. 2008). It is probably also present in Hawai‘i, where it has been confused with P. scrobiculatum (Snow 2010).

Paspalum thunbergii has some economic importance, since it is sometimes planted for erosion and desertification control or for afforestation purposes (Quattrocchi 2006). However, it is also a reputed weed species (e.g. Holm & al. 1979; Häfliger & Scholz 1980; Watson & Dallwitz 1992), mostly in paddy fields (e.g. Moody 1989), but also in sugar cane, for instance in Taiwan (Peng 1984).

It is not clear how Paspalum thunbergii arrived in Italy. Although it has some economic importance, in Italy an accidental introduction seems more likely. In Boscaccio the forest path leads to a fish pond where the Chinese pond mussel (Sinanodonta woodiana Lea) was recently introduced. This species is known to have entered Europe with, among others, Chinese fish such as silver carp, Hypophthalmichthys molitrix Valenciennes (Cappelletti & al. 2009). It is remarkable that apparently in the same period a grass species native to China emerged in the same area. Alternatively, forestry work in the nearby heathland may also have been responsible for the inadvertent introduction of P. thunbergii in Boscaccio (by propagules adhered to the forestry machines). In the latter case, it should occur elsewhere in the area as well. The vector of introduction in the Mortara locality is not clear, but it is probable that it arrived along with rice seeds (this species is recorded from wet soils, including paddy fields, in China). The species was surely not introduced for revegetation of the channel embankment, since rice growers in the Lombardia and Piemonte regions prefer bare embankments and rice field margins that are devoid of any kind of vegetation, weedy or not.

According to the criteria defined by Richardson & al. (2000), in Italy Paspalum thunbergii is regarded as a naturalized species on the basis of current data.

Selected specimens examined

Italy: Lombardia: Pavia province, Mortara, strada Cascina Gianolo all'altezza dell'omonima cascina (CFCE 0718-1:Mortara), UTM ED50: 32T 0477413.5012041, 109 m, sponda di fossato, copioso, 20 Jul 2011, N. Ardenghi 43241, 43242 (MSNM [sub P. dilatatum]); ibid., 45°15′32.3″N, 08°42′49.0″E, 110 m, between an unsurfaced road and a rice field channel embankment, wet compacted sandy soil, 12 Aug 2015, N. Ardenghi & S. Mossini s.n. (BR); Monza and Brianza province, Boscaccio, municipality of Lentate sul Seveso, 45°4133.1″N, 09°08′38.9″E, 280 m, along a path in a woodland of Quercus robur and Pinus sylvestris, near a road, acid (heathland ecosystem), 2 Oct 2014, G. Brusa s.n. (BR). — China: Guizhou: Jiangkou Xian, Heiwan River at Tongkuangchang, SE side of the Fanjing Shan mountain range, river flood plain and adjacent mixed-deciduous broad-leaved evergreen forest on steep slopes, c. 900 m, growing in weedy area along trailside with Plantago, 27 Aug 1986, Sino-American Guizhou Botanical Expedition 551 (BR). — Japan: Hondo, Noda in Shimosa, 28 Aug 1950, J. Ohwi 64 (BR); Yokoska, Savatier 1866-74 (BR, [dupl. P n.v.]); Yokohama, 1862, Maximowicz Iter secundum (BR, [dupl. LE n.v.]).