Stachys byzantina K. Koch (SW-As.) – A rare and usually ephemeral escape from cultivation or garden throw-out, sometimes temporarily persisting or locally more or less naturalized. Much grown in gardens in Belgium (although perhaps slightly decreasing lately) but relatively rarely escaping. Probably first recorded on rocky slopes in Malonne in 1882. Soon afterwards also seen on dry rocky slopes in Modave (1891-1893) and Lamprez (1904). All these records are from surprisingly natural habitats (but probably close to habitations). In the 20th and 21th century more regularly seen, also on dumps, ground heaps or on waste land, for instance in Les Avins (1978), Petigny (1983), Hoboken (2005) or Moorsele (2009). Recently also seen on the calcareous slopes adjacent to the Albertkanaal in Veldwezelt (2006) and along river Meuse in Godinne (2008). Recorded on the old city walls in Binche in 1959. Probably widely neglected elsewhere although well-established populations seem to be scarce (for instance in dry grassland in Genk, see: http://waarnemingen.be/waarneming/view/55178006. Up-to-date information about its presence in Belgium, including a distribution map, is available here: http://waarnemingen.be/soort/view/20619.
Stachys byzantina is part of the S. germanica group, a monophyletic assemblage of closely related species (see also Falciani 1997, Dündar & al. 2013). Out of this complex four species have been recorded in Belgium (two native and two introduced). Stachys byzantina is most closely related to S. cretica. Both are eglandular and have leaves with a cuneate to truncate base. However, as a rule, Stachys cretica tends to be slightly less tomentose (upper leaf surface more or less visible, not entirely obscured by the tomentose indumentum), its leaves are less cuneate at base (the lowermost often truncate to almost rounded) and often narrower and its calyx teeth are slightly longer and narrower (about ½ as long as tube versus 1/3 as long as tube in Stachys byzantina).
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Selected literature:
Dündar E., Akçiçek E., Dirmenci T. & Akgün Ş. (2013) Phylogenetic analysis of the genus Stachys sect. Eriostomum (Lamiaceae) in Turkey based on nuclear ribosomal ITS sequences. Turk. J. Bot. 37: 14-23. [available online at: http://journals.tubitak.gov.tr/botany/issues/bot-13-37-1/bot-37-1-2-1203-26.pdf]
Falciani L. (1997). Systematic Revision of Stachys Sect. Eriostomum (Hoffmans.&Link) Dumort. in Italy. Lagascalia 19(1-2): 187-238. [available online at: http://institucional.us.es/revistas/lagascalia/19/Systematic%20Falciani.pdf]
Leslie A.C. (1993) Plant portraits from the Lindley Library: Stachys byzantina. The Garden 118: 240-242.