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Ehrharta longiflora Sm. and Pennisetum setaceum (Forsk.) Chiov., two new alien grasses for Madeira Island (Portugal)

The number of introduced, and possible introduced, taxa in the Madeira and Selvagens islands currently accounts for nearly 36% of the total flora of these archipelagos, including 53 Poaceae taxa (out of 141 Poaceae taxa), therefore constituting the family with the higher proportion of introduced taxa (38.4%). The genus Ehrharta Thunb. comprises about 35 species, with one species, E. longiflora Sm., recorded as introduced in Gran Canaria. The genus Pennisetum Rich. includes ca. 80 species of which a total of nine species are present in Macaronesia, with three: P. clandestinum Hochst. & Chiov., P. purpureum Schum. and P. villosum R. Br. ex Fresen, occurring in the Madeira archipelago. Ehrharta longiflora Sm. and Pennisetum setaceum (Forssk.) Chiov., are here recorded for the first time for the Madeira island, found in disturbed areas at low and medium altitudes. The finding of several mature and flowering/fructifying individuals of both species suggests a fully naturalized status. Naturalization, invasiveness and ecological impacts are discussed.


INTRODUCTION
The archipelagos of Madeira and Selvagens include 1204 taxa of vascular plants, including 401 introduced taxa and 29 as possible introduced (Jardim and Menezes de Sequeira 2008). In what concerns the grass family, more than one third correspond to alien taxa, i.e. 54 out of 141 (Jardim and Menezes de Sequeira 2008), corresponding to almost 12% of the total number of introduced vascular plant taxa.
Pennisetum Rich. is a cosmopolitan tropical genus that includes about 80 species native from Africa (Fish et al. 2015). A total of 9 species of this genus are already reported in the Macaronesian archipelagos, 7 of them as aliens:  Ginóves et al. 2009;Silva et al. 2010;Verloove 2013). There is also a reference to Pennisetum macrourum Trin. for the Canary Islands as cultivated and occurring spontaneous in one locality in Las Palmas .
The segregation of the genera Pennisetum and Cenchrus L. has always been controversial. Diagnostic morphological characters being the degree of fusion of bristles and their characteristics, and the presence of pedicellate spikelets, however none of these characters can fully differentiate them (Chemisquy et al. 2010). Although some authors still consider Pennisetum and Cenchrus as two separate genera (Fish et al. 2015), recent molecular studies suggest otherwise (Donadío et al. 2009). Chemisquy et al. (2010, also based on molecular data, propose the inclusion of both Odontelytrum Hack. and Pennisetum in the genus Cenchrus. Pennisetum clandestinum, was included in a separate genus -Kikuyuochloa H. Scholz (Scholz, 2006), but included in Cenchrus by other authors (Verloove 2012;Veldkamp 2014). The taxonomic and nomenclatural criteria adopted here follow Jardim and Menezes de Sequeira (2008). Pennisetum setaceum native distribution ranges from North Africa to the Middle East (Fish et al. 2015). In Europe, it is present as alien species in the south of the Iberian Peninsula, Canary archipelago and Sicily (Valdés and Scholz 2009). In Portugal, P. setaceum is naturalized in Alto Alentejo (Bejarano et al. 2011), Algarve (Marchante et al. 2014), and Extremadura (Gullón 2017).
Pennisetum setaceum was introduced as ornamental plant in the Canary Islands in the 40's (Saavedra and Alcántara 2017) and found naturalized in different locations in the north of Tenerife in 1969 (Hansen 1970). It is currently present in all the islands of the archipelago, prevailing below 500 m a.s.l., affecting the coastal xerophytic scrub and the endemic communities dominated by Euphorbia canariensis L. and E. balsamifera Aiton (González-Rodríguez et al. 2010). P. setaceum also outcompetes native grasses (e.g. Hyparrhenia hirta (L.) Stapf, Aristida adscensionis (L.), and affects the native rupicolous flora (Elorza et al. 2004;González-Rodríguez et al. 2010;Anonymous 2014).
Due to its fast growth and high capacity to adapt to different habitat conditions (Elorza et al. 2004), P. setaceum was recently included on the List of Invasive Species of Union Concern (EU 2017). Previously, this species was also included in the Spanish Catalogue of Invasive Alien Species, what entails in the "prohibition generic possession, transport, trafficking and trade of live or dead specimens, their remains or propagules, including foreign trade" (Anonymous 2014). Despite the conservation concerns, P. setaceum continues to be cultivated in many regions as ornamental plant (Gullón et al. 2017).
The genus Ehrharta Thunb. includes about 35 species, naturally distributed from South Africa to Ethiopia and Yemen (Fish et al. 2015). Four species of this genus: E. calycina Sm., E. delicatula Stapf, E. erecta Lam. and E. longiflora Sm., are present in Europe and North Africa (Morocco and Tunisia) as alien species (Valdés and Scholz 2009). E. longiflora was reported for Gran Canaria as naturalized for the first time by Kunkel (1978), as probably escape from cultivation, in a medium altitude (650 m a.s.l.), moist and shady habitat. In fact, E. longiflora is a palatable species for cattle, known to have a high leaf production (Fish et al. 2015).
Here we present the first record of E. longiflora and P. setaceum for the archipelago of Madeira. Naturalization, invasiveness and ecological impacts of both species are also discussed.

MATERIAL AND METHODS
Collected specimens where stored in the herbarium of the University of Madeira and identified using descriptions and keys published by Kellogg (2015) and Fish et al. (2015). During fieldwork, 2018 and 2019, collection sites were briefly characterized including: the approximate number of individuals of both species, the dominant plant taxa, exposure, slope and altitude (Table 1). The distribution map (Figure 1) was produced using ArcGis online version E204CW. The two species occurred in disturbed areas highly exposed to the sun. Fully developed flowering and fructifying individuals of both species were found (Figures 2, 3, 4 and 5).  a road (Figure 2), but also in cliffs and basaltic walls (Figure 3) including on a margin of a small brook, corresponding to highly hemerobic areas close to roads, houses and gardens. P. setaceum was the dominant plant, although this dominance was shared, in some cases, with other alien plants such as Pennisetum clandestinum, Ageratina adenophora (Spreng.) R.M. King & H. Rob. and Cardiospermum grandiflorum Sw. Cosentinia vellea (Aiton) Tod. (Table 1), a rare native fern in Madeira island, was found in chasmophytic invaded habitats.  One individual of Pennisetum setaceum was found on a cliff near the ocean in Funchal (São Martinho), next to a pedestrian path and with no gardens nearby, on a community dominated by Cenchrus ciliaris L., Nicotiana glauca R.C. Graham and Sinapidendron angustifolium (DC.) Lowe (table 1). After the first visit, the specimen was eventually removed, and no other individuals were found in the surrounding area.
Pennisetum Rich. key to the Madeira archipelago species:  One population of E. longiflora was found in Calheta (Ponta do Pargo) (figure 1) along a roadside close to agriculture fields occupying, so far, a very restricted area, dominated by P. clandestinum (table 1). This population included several mature individuals (figures 4 and 5) suggesting a fully, although localized, naturalization. In June, one month after the first visit, plants were subject to mowing, therefore no photographs of the naturalization site were taken.

DISCUSSION
Pennisetum setaceum was probably introduced in Madeira island as ornamental plant, considering that this species is used in many parts of the world for this purpose and is often found in nurseries (Salinas et al. 2011;Saavedra et al. 2014;GIDS 2015;Gullón et al. 2017). P. setaceum is a perennial C4 plant and, consequently, can withstand dryness and high temperatures, being widely used as garden plant (Rahlao et al. 2010). Sometimes, it is also used for the stabilization of soil and cliffs (Salinas et al. 2011). These characteristics, along with ecological adaptability, rapid growth and high seed production (100 seeds per plant), make it a species with high invasive potential (EPPO 2012).
So far Pennisetum setaceum has a relatively small area of distribution on Madeira island, but according to Dana et al. (2005) fruits are easily dispersed, by water, animals, people and even cars, being therefore highly probable that this alien grass will spread quickly to other areas. Salinas et al. (2011) also refer that fruits are easily dispersed and to the fact that fruits remain viable in the soil for 6 years or more, being also capable of sprouting from root fragments.  Pennisetum setaceum prevails on arid and semi-arid open areas GISD 2015), and, therefore, Madeiran Mediterranean secondary grass communities (e.g. Dactylo hylodes-Hyparrhenietum sinaicae, Cenchro ciliaris-Hyparrhenietum sinaicae and Bromo-Oryzopsion miliacei, as defined by Capelo et al. 2004) could be invaded by this grass. If this invasion occurs, it will possibly block successional processes, therefore affecting endemic communities such as Euphorbietum piscatorie. P. setaceum will also potentially affect chasmophytic plant communities (e.g. Sedo nudi-Aeonietum glutinosi). Salinas et al. (2011) describe the elimination by competition, of native and endemic species, but also changes in soil carbon sequestration, that further affect succession. In the Canary Islands P. setaceum can reach altitudes above 1000 m a.s.l. Salinas et al. 2011), but it seems to be limited to areas with an average annual rainfall of less than 1270 mm/m 2 (GISD 2015), not tolerating freezing temperatures (Devender 1997). These data suggest that the south coast and the east side of the island of Madeira are likely to be invaded and that most of the north coast and the mountain areas are less likely to be affected.
Due to the large amount of biomass accumulated, P. setaceum potentiates the risk of fires, which further increases its expansion (Salinas et al. 2011).
Ehrharta longiflora was probably introduced for cattle feeding (see Fish et al. 2015), since it was found naturalized near agricultural fields. The dispersion of E. longiflora mainly occurs locally and is wind mediated, but fruits may also be dispersed by animals (Frey 2005). This species is already recorded as naturalized in several countries of North Africa and Europe, including Spain (Valdés and Scholz 2009) and being reported as invasive in Australia, New Zeeland and California (Frey 2005).
Ehrharta longiflora typically occurs in wet shady places (near rocks and shrubs), often near disturbed areas (e.g. gardens, roadsides), but is also found in hill slopes (Fish et al. 2015). Apparently, the invasion of this and other Ehrharta spp. is facilitated by moisture. Besides that, these species can tolerate extensive annual summers in Mediterranean climates due to their deep-roots (Frey 2005).
In Madeira, E. longiflora possibly will prevail in areas of medium altitude, such as occurs in the Canary Islands (Kunkel 1978), but its invasiveness is hard to predict due to the scarcity of available information. Irrigated disturbed areas could be at higher risk of invasion, but this species may disperse to areas of high conservation value, possibly including laurisilva clearings and margins.
As in the islands of El Hierro, La Gomera, Fuerteventura and Lanzarote, where the introduction of P. setaceum was later (in the 1990s) (Garcia-Gallo et al. 1999) and where control is still approachable, monitorization of populations and quick intervention (eradication) seems to be the best strategies and should be applied for Madeira. According with Garcia-Gallo et al. (1999) the removal of individuals, manually or using hoes, seems to be the most effective method of eradication of P. setaceum (and has been applied in many parts of the world). It is important to eliminate the floral parts first by carefully covering the inflorescences with plastic bags, and removing all root fragments and seeds that are present in the soil (Garcia-Gallo et al. 1999). Chemical methods may be implemented in situations where the complete removal of individuals is not possible (walls, asphalt) using systemic herbicides such as hexazinone or similar products, since glyphosate appears to be ineffective (Anonymous 2014).
Although both taxa may become troublesome invasive, Pennisetum setaceum constitutes a clear threat to Madeira ecosystems. P. setaceum is still in an initial phase of invasion and plants should be eradicated urgently, and its use as ornamental prohibited.

ACKNOWLEDGMENTS
The authors are grateful to the IFCN (Instituto das Florestas e Conservação da Natureza, IP-RAM) for the collecting permit