Centaurea alba
Centaurea alba is a species of "Centaurea" found in the Iberian Peninsula in southern and central Spain and in a small neighbouring area in the interior of Portugal. There are three recognised subspecies, and of one subspecies, the nominate, there are furthermore three varieties. It has been called pale knapweed in English. Vernacular names which have been recorded for this herb in Castilian Spanish are "calcitrapa", "cardo estrellado", "centaura estrellada", "garbanzos del cura", "siempre nueva", "siempre-nueva", and "trapacaballos". Other local recorded names in Spanish are "abreojos", "abrepuños", "amargosa", "amargosilla", "amargoso", "ardolla", "arzolla", "cardo abrepuños", "cardo de la  arzolla", "marbosilla", "margosilla", "piropo", "planta para hemorroides" and "raíz de la arzolla". In the Catalan language it is known as "raspallera" in the Valencian dialect. Taxonomy. The species was first described in the modern Linnaean system by Linnaeus himself in the first edition of the Species Plantarum, published in 1753. It is presently placed in Augustin Pyramus de Candolle's section or subsection "Phalolepis", along with "Centaurea costae" and the much more widely distributed "C. deusta". In 2014 Hilpold "et al". redefined the infrageneric taxa, classifying the traditional section "Phalolepis" in the subgenus "Centaurea". Formerly the genus "Centaurea" was paraphyletic , because it was based on a species, "C. centaurium" -the type species, which was less related to the vast majority of other "Centaurea" than to species which were classified as belonging to other genera. In 2001 Werner Greuter solved this by moving the "C. centaurium" to the old, resurrected genus "Rhaponticoides", conserving the name "Centaurea" for the majority of the other species, and electing "C. paniculata" to serve as the new type species. The infraspecific taxonomy has been rather volatile since the 1970s. A large number of former subspecies were recognised at one time or another. These were synonymised over  the last century or so, or are now considered independent species. In his 1976 contribution in the "Flora Europaea", Josef Dostál recognised subsp. "albanica", subsp. "brunnea", subsp. "costae", subsp. "deusta", subsp. "formanekii", subsp. "latronum" and subsp. "subciliaris". A lectotype was assigned by Salvador Talavera Lozano in 1984. The 2006 entry by Greuter in the Euro+Med Plantbase, based on a critical evaluation of the information from the "Flora Europaea" and the "Med-Checklist", recognised the following infraspecific taxa: In 2008 the chromosomes of the different infraspecific taxa were investigated (karyotypy). All forms are 2"n"=18, but some differences between the taxa is  seen in the chromosome morphology. The species was revised again in 2011. The 2014 entry in the "Flora Ibérica" follows this interpretation, although it only briefly mentions the three varieties. The name "C. deusta", a species more widely distributed in southern Italy, Greece and Turkey, has also historically been mistakenly said to occur in Spain, for example by Augustin Pyramus de Candolle in 1838 in the "Prodromus", in the 1865 issue of the "Prodromus Florae Hispanicae" of Heinrich Moritz Willkomm and Johan Lange, or by Carl Fredrik Nyman in his "Conspectus Florae Europaeae" (1878-1884). Dostál subsumed "C. deusta" in  the "Flora Europaea" as "C. alba" subsp. "deusta", and this taxon continued to be recognised as occurring in Spain in the 2001 entry in the "Atlas de la flora del Pirineo Aragonés". Hybrids. All of the species in the subgenus "Centaurea" appear to be able to hybridise freely with each other, and "C. alba" is no exception. In some, but not all, of the zones where the following taxa are in contact with "C. alba", the following natural hybrids have been described as occurring. A cross of the nominate form with "C. langei" subsp. "kheilii" creates the hybrid "C." ×"bigerrensis , and with C. aristata", "C." ×"matritensis" is created. The variety "latronum" is also known to cross with "C. calcitra", creating "C." ×"eliasii", recognisable by having its involucral bracts being tipped by a large and sharp spine. Another hybrid of the species has also recently (2009) been described from a 1988 collection in an industrial zone in the Province of Soria: "Centaurea" ×"soriana" . The other parent of the hybrid is "C. paniculata" subsp. "castellana". Lastly, in the Province of Soria relatively frequently transitional forms between the nominate variety "alba" with "C. alba" subsp. "aristifera" can be encountered. Description. It is most  similar to "Centaurea costae", being mainly distinguished by the shape of the involucral bracts. "C. costae" has bilobed bracts. Distribution. It only occurs on the Iberian Peninsula, being found at generally inland sites in central, central-north, central-western y southwestern parts of the Peninsula. In Spain it is found in the provinces of Ávila, Badajoz, Burgos, Cádiz, Cáceres, Ciudad Real, Cuenca, Guadalajara, Huelva, León, Madrid, Salamanca, Sevilla, Segovia, Soria, Toledo, Valladolid, Zaragoza and Zamora. In Portugal it occurs in Beira Baixa and Ribatejo Province. The different subspecies and varieties now recognised are largely not sympatric and have discreet geographical  distributions. Two taxa have disjunct distributions, subsp. "tartesiana" to the south of the main distribution, and var. "macrocephala" further to the south of that, at the southernmost tip of continental Spain. For a long time it was believed to grow in northeast Algeria. According to López this was originally based on a single sheet of a specimen in the personal herbarium of Georges Rouy, collected in Segovia in 1905, but apparently accidentally included in the section "Plantes d’Algérie" of the herbarium. It is one of five duplicates, one of which is the lectotype of the subspecies "alba" synonym "Centaurea segoviensis . However, C. alba" var. "mauritanica" had already been described by Jules Aimé Battandier in his 1889 "Flore de l'Algérie" as growing in Algeria, and an Algerian population of "Centaurea" was called as "C. alba" in the local flora until the 2000s, for example in the 1963 "Nouvelle flore d'Algérie", or the 1985 French collection on the Djebel Ich Ali near Tazoult in Batna wilaya. This population is now seen as a synonym of "C. djebel-amouri", which was only recently described as a new species by Greuter in 2003; the previous name "C. alba" for the population is now attributed  as "auct. Afr. N. non L.". Plants from Italy, France and possibly Albania have also historically been misidentified as "C. alba". Ecology. It blooms from April to October. This species inhabits woodland clearings and the fringes of forests, especially pine forests, oak forests and "melojares" ("Quercus pyrenaica" forests), as well as growing in matorral, wasteland and gutters, slopes and wayside verge habitat along roads. It has been recorded growing at 3 to 2,000 metres in altitude. It prefers somewhat fertile soils, or not excessively fertilised, which can be acidic to alkaline. It is usually found growing in rocky, large-grained  soil, very often calcarous mixed with silicates. The "macrocephala" variety occurs in matorral habitats on substrates derived from calcarenite and limestone. The "tartesiana" subspecies occurs in slate-based soils and marl. Conservation. In 1992 two subspecies, subsp. "heldreichii" and subsp. "princeps", were designated as 'priority species' under Annex II of the Habitats Directive of the European Community (which was reformed as the European Union the following year). This designation was meant to serve as the basis for Spain to declare which areas in which it occurs were 'Special Areas of Conservation' -which were to form the backbone of the Natura  2000 network, but only if these areas include one of the number of habitats listed in Annex I of the directive. Neither subspecies are still recognised. In 2005 the flora of Andalusia was assessed for the "Lista roja de la flora vascular de Andalucía", with two subspecies, subsp. "tartesiana" and subsp. "macrocephala", being included in the list. These two taxa were assessed as 'data deficient', but were included because they have restricted distributions and the authors thought that they might be threatened, or at least impacted, by changes in agriculture.