Centaurea alba

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. These were synonymised over the last century or so, or are now considered independent species. • Centaurea alba subsp. albanica (Halácsy) Dostál - a taxon from Albania. • Centaurea alba subsp. brunnea (Halácsy) Dostál • Centaurea alba subsp. ciliata (Font Quer ex O.Bolòs & Vigo) Greuter • Centaurea alba subsp. costae (Willk.) Dostál • Centaurea alba subsp. formanekii (Halácsy) Dostál • Centaurea alba subsp. latronum (Pau) Dostál • Centaurea alba subsp. macrocephala (Pau) Talavera • Centaurea alba subsp. maluqueri (Font Quer) Molero & Vigo • Centaurea alba subsp. montsicciana (Pau & Font Quer) Romo • Centaurea alba subsp. strepens (Hoffmanns. & Link) Rocha Afonso • Centaurea alba subsp. subciliaris (Boiss. & Heldr.) Dostál • Centaurea alba subsp. tartesiana Talavera 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. 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. • Centaurea alba subsp. alba - • Centaurea alba subsp. aristifera - • Centaurea alba subsp. tartesiana - ==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. 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. • Centaurea alba subsp. aristifera - • Centaurea alba subsp. tartesiana - An endemic of the northwest corner of Andalusia. It occurs in the western part of the Sierra Morena mountain range, in the provinces of Huelva and Sevilla. ==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 calcareous 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. ==References==