Dracocephalum L.
Dracocephalum is, in its traditional circumscription, a genus of ca. 70 species, mostly native to temperate Asia (one species in North America) (Mabberley 2008). About half of the known species occurs either in China (Li & Hedge 1994) or in the former USSR (Shishkin 1977). Some species are cultivated as ornamentals (see Knees 2000 and Jäger & al. 2008 for a recent account of the genus in European gardens). Dracocephalum is furthermore reputed for medical purposes or as bee plant. One species, Dracocephalum parviflorum, is a weed of arable land and ruderal places.
Lallemantia (see there) is very closely related to Dracocephalum (many species have names in both genera). It is distinguished by two longitudinal folds within the upper lip of the corolla in which the stamens are concealed. Nepeta is also similar but in this genus calyx teeth are more or less equal, not distinctly 2-lipped.
In its current circumscription, Dracocephalum was shown to be not monophyletic (Bräuchler & al. 2010). Hyssopus (although morphologically very different) and perhaps also Lallemantia are imbedded in it (Drew & Sytsma 2012).
1 Leaves nearly glabrous. Corolla 20-25 mm long, much longer than the calyx === Dracocephalum moldavica
Leaves more or less hairy. Corolla 12-20 mm long, hardly exceeding the calyx === 2
2 Inflorescence verticillate (6-12 or more flowers), interrupted below and more congested above. Corolla 7-9 mm long, lilac. Bracts entire === D. thymiflorum
Inflorescence very compact and uninterrupted, with numerous flowers. Corolla slightly longer, 12-20 mm long, white or very pale blue. Bracts pectinate, with sharp pointed teeth === D. parviflorum
Literature:
Bräuchler C., Meimberg H. & Heubl G. (2010) Molecular phylogeny of Menthinae (Lamiaceae, Nepetoideae, Mentheae) -Taxonomy, biogeography and conflicts. Molecular Phylogenetics and Evolution 55(2): 501-523.
Budantsev A.L. (1987) Sistema roda Dracocephalum (Lamiaceae). Bot. Žhurn. 72: 260-267.
Budantsev A.L. (1990) Konspekt roda Dracocephalum L. (Lamiaceae): 2. Novosti Sist. Vyssh. Rast. 27: 125-135.
Budantsev A.L. (1993) Konspekt triby Nepeteae (Lamiaceae): rody Lophanthus, Dracocephalum, Cedronella, Schizonepeta i Agastache. Bot. Zhurn. 78(2): 106-115.
De Wolf G.P. (1955) Notes on cultivated Labiates. 7. Dracocephalum. Baileya 3: 115-129.
Drew B.T. & Sytsma K.J. (2012) Phylogenetics, biogeography, and staminal evolution in the tribe Mentheae (Lamiaceae). Am. J. Bot. 99(5): 933-953. [available online at: http://www.amjbot.org/content/99/5/933.long?cited-by=yes&legid=amjbot;99/5/933&related-urls=yes&legid=amjbot;99/5/933]
Heywood V.H. (1972) Dracocephalum. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 161.
Institute of Biology, Soil and Desert, of Sinkiang. (1975) The genus Dracocephalum L. in Prov. Sinkiang, China. Acta Phytotax. Sin. 13(1): 19-52.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Kaufmann M. & Wink M. (1994) Molecular systematics of the nepetoideae (family Labiatae): phylogenetic implications from rbcL gene sequences. Z. Naturforsch. C. 49(9-10): 635-645.
Keenan J. (1957) Notes on Dracocephalum. Baileya 5: 25-44.
Knees S.G. (2000) Dracocephalum. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 221-223.
Li H.-W. & Hedge I.C. (1994) Dracocephalum. In: Wu Z.-Y. & Raven P.H. (eds.), Flora of China, vol. 17. Bejing, Science Press: 124-133. [available online at: http://flora.huh.harvard.edu/china/PDF/PDF17/dracocephalum.pdf]
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Shishkin B.K. (1977) Dracocephalum. In: Shishkin B.K. (ed.), Flora of the U.S.S.R., vol. XX. Academy of Sciences of the USSR: 295-318.