Further naturalised Cactaceae in northeastern Iberian Peninsula by

During the floristic work carried out in 2004 in the Baix Camp region of Tarragona (NE Spain) we found four new species of alien naturalised Cactaceae. Of these, three are reported for the second time from Europe and the other is new to Catalonia region. Southern Catalonia, with eleven species of Cactaceae, harbours the highest diversity of the family in Europe. Our results demonstrate that this diversity is even higher than previously believed. The introduction of these exotic taxa is, once again, due to the development of gardening based exclusively on foreign elements, to the unscrupulous and uncontrolled dumping of their remains in the natural environment, and to the existence of a


Introduction
In the summer of 2004 the systematic prospecting for alien plants in the southern coast of Tarragona was completed (Sobrino & al., 2002).The area is particularly rich in Cactaceae, as we already showed in a previous paper (Sanz-Elorza & al., 2004).With these new findings, the number of species of this family in northeastern Iberian Peninsula reaches eleven.This is a strikingly high number, as except for the American regions from where these species are native, no other place in the world is known to have such a diversity of Cactaceae.
The botanical exploration for this study was designed by the Group of Alien Plant Species of the Spanish Society of Weed Science (Sobrino & al., 1999) to report the presence and distribution of alien species in Spain, and has been carried out during the last five years.With this study, the floristic prospecting of the dry river beds in the coastal areas of Tarragona between Cambrils and the estuary of the Ebro river has been completed.The study has been focused in Cactaceae because of its abundance and marked invasory character of several of its species (Richardson & al., 2000).With respect to the demography, we basically follow the methodology proposed by Iriondo (2001), while for the characterisation of the natural environment we follow Sanz-Elorza & al. (2004).er bed, 41º05'14''N, 1º02'43''E, (31TCF3550), 30 m, 20-VIII-2004, M. Sanz-Elorza (MA 720829).
Demography: The population consists of three individual adults forming a complex tangle of vegetation and at least ten young plants established from loose joints.The population occupies an area of 20 m 2 on the left bank of L'Alforja river, facing south, near to the place where the A7 motorway bridge crosses the river.In the same area other Cactaceae (Austrocylindropuntia subulata, Opuntia engelmannii, O. ficusindica, O. lindheimeri, and O. monacantha) cohabit with native elements like Hyparrhenia hirta, Pinus halepensis, Piptatherum miliaceum, Pistacia lentiscus, Ulex parviflorus, etc.
Flowering time in Spain for this species is unknown, as there is not enough phenological information, although during our visit (August) there were some flowers open.It is an extremely estenocorous taxon, only known as a dubious native plant near San Antonio (Texas, USA), where it may even have become extinct (Benson, 1982: 495;Anderson, 2001: 498), and Bexar County, also in Texas (Weniger, 1984;Pinkava, 2003: 136).In 1908 Griffiths introduced its cultivation and since then it is one of the "Chollas" most used in gardening because of its curious long  blades (Benson, 1982).It is also relatively common as naturalised in different places in USA and Mexico (Pinkava, 2003).The systematic position of this taxon has been subject to some controversy: authors like Britton & Rose (1919: 164) and Backeberg (1977: 366) consider it an independent species, whilst others (e.gr., Bravo-Hollis, 1978: 286-289;Benson, 1982: 495-496)   The variegate form of this species has been recently reported from the Baix Camp (Sanz-Elorza & al., 2004).Now this species has been found again in its typical form in other site of the "riera de l'Alforja", four kilometers away of the previous population, which confirms the stable presence of the species in southern Catalonia.The presence of both expressions (typical and variegate) and the large size of the specimens suggest that they are the result of old and independent introductions.

Demography:
The population consists of a young individual 2.5 m high branched almost from the base and four young plants growing from loose joints.The population occupies an area of 40 m 2 on the left bank of the l'Alforja river, facing south, near the place where the A7 motorway bridge crosses the river.It grows with several species of Cactaceae (Austrocylindropuntia subulata, Cylindropuntia imbricata, Opuntia engelmannii, O. ficus-indica, and O. lindheimeri) and other alien species (Agave americana, and Araujia sericifera) in a Hyparrhenia hirta, Pinus halepensis, Piptatherum miliaceum, Pistacia lentiscus, Ulex parviflorus, etc. formation.
The native area of this taxon includes the deserts of northern Mexico (Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, and Zacatecas), south to the state of Hidalgo (Bravo-Hollis, 1978: 243;Anderson, 2001: 508), and it has been introduced in Arizona (Pinkava, 2003: 142).Several varieties have been described based on the shape and size of the joints and the colour of the glochids.It is a very decorative plant, easy to cultivate and popular in gardening.This is the first record of the plant in Catalonia.Previously, both var.albispina Fobe and var.microdasys had been reported from Valencia (Guillot & Van der Meer, 2001: 41;Guillot, 2003: 11) and Castellón (Guillot, 2003) provinces.

Demography:
The population consists of an undetermined number of young individuals coming from gardening remains dumped and partially buried in the river l'Alforja.It occupies an area of 10 m 2 on the left bank of l'Alforja river, facing south, near the junction of the A7 motorway.It grows close to several very large plants of Austrocylindropuntia subulata and Opuntia ficus-indica, as well as other alien species (Agave americana, Araujia sericifera, and Senecio angulatus).

Discussion
Just along one of the dry river beds of the Tarragona province (NE Spain) we have found four different species of Cactaceae, which, with the eight already known (Sanz-Elorza & al., 2004), represent the highest diversity of Cactaceae on a local scale recorded so far for all Catalonia, Iberian Peninsula, and even Europe.
Once again, the combination of xerogardening based on exotic species, intense human pressure on the territory with the resulting destruction or degradation of the pre-existing vegetation and the particularly benign climatic conditions have favored the introduction and establishment of several Cactaceae in an area where alien elements are particularly dominant in the flora.
As it has been already pointed out (Sanz-Elorza & al., 2004), the process of invasion of the southern coast of Catalonia by exotic vascular plants is an unstoppable process.This invasion processes should be explicitly included in the design of biodiversity conservation strategies in those regions which are especially sensitive and vulnerable (Dana & al., 2003(Dana & al., : 1009)).