Verbena

Verbena, as currently circumscribed (see for instance Sanders 2001), is a genus of ca. 50 species. It traditionally falls apart into two more or less distinct sections: section Verbena with most representatives in North America and section Pachystachyae Schauer with chiefly South American species. Non-native taxa of both sections occur in Belgium and one species, Verbena officinalis L., is native. Nesom (2010) recently proposed a slightly modified infrageneric classification. Several species of Verbena are cultivated as ornamentals (Wann 2000) and some are reputed environmental or agricultural weeds.

1. Stem prostrate or procumbent to decumbent-ascending. Bracts much longer than the calyx, foliaceous, ca. 8-15 mm long === Verbena bracteata

1. Stem erect. Bracts shorter than or about equaling calyx, ca. 1-3 mm long === 2

2. Inflorescence of compound cymes. Spikes thick and compact, not exceeding 20 cm and scarcely elongating after anthesis. Fruits very closely congested along rachis === 3

2. Inflorescence a solitary spike or a simple cyme. Spikes thin and rather lax, up to 40 cm long and much elongating after anthesis. Fruits often remotely arranged along rachis (except in V. hastata) === 5

3. Leaves narrowly tapering into a cuneate-attenuate base, (sub-) petiolate === V. brasiliensis

3. Leaves sessile, rounded to almost cordate at base, often more or less semi-amplexicaul === 4

4. Bracts shorter than the calyx. Robust plant, up to 200 cm tall. Leaves herbaceous, not very rigid. Inflorescence much branched with comparatively slender spikes === V. bonariensis

4. Bracts longer than the calyx. Lower plant, rarely exceeding 60 cm. Leaves coriaceous and rigid. Inflorescence usually in subternate groups with thick spikes, (5-) 10-15(-20) mm diameter === V. rigida  

5. Lower leaves deeply pinnately lobed (native) === V. officinalis

5. Lower leaves serrate or shallowly lobed === 6

6. Spike stiffly erect, fruits imbricate. Corolla blue-violet. Lower leaves sometimes lobed or hastate === V. hastata

6. Spike very slender, filiform, fruits very remotely arranged. Corolla white. Lower leaves never lobed === V. urticifolia

 

Additional aliens: Verbena halei Small (incl. V. gaudichaudii (Briq.) P.W. Michael, syn.: V. officinalis L. var. gaudichaudii Briq.) (N-Am., wool alien) and V. supina L. (Medit., wool alien).


Literature

Barber S. (1982) Taxonomic studies in the Verbena stricta complex (Verbenaceae). Syst. Bot. 7: 433-456.

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.

Moldenke H.N. (1961) Materials towards a monograph of the genus Verbena. Phytologia 8: 108-496.

Munir A.A. (2002) A taxonomic revision of the genus Verbena L. (Verbenaceae) in Australia. J. Adelaide Bot. Gard. 20: 21-103.

Nesom G.L. (2010) Infrageneric classification of Verbena (Verbenaceae). Phytoneuron 2010-11: 1-15.

O’Leary N., Múlgura M.E. & Morrone O. (2007) Revisión taxonómica de las especies del género Verbena (Verbenaceae): serie Pachystachyae. Ann. Missouri Bot. Gard. 94: 571-622.

O’Leary N., Múlgura M.E. & Morrone O. (2010) Revisión taxonómica de las especies del género Verbena (Verbenaceae) II: serie Verbena. Ann. Missouri Bot. Gard. 97: 365-424.

Perry L.M. (1933) A revision of the North American species of Verbena. Ann. Missouri Bot. Gard. 20(2): 239-363.

Sanders R.W. (2001) The genera of Verbenaceae in the Southeastern United States. Harvard Papers Bot. 5(2): 303-358.

Sell P. & Murrell G. (2006) Flora of Great Britain and Ireland. Vol. 4 Campanulaceae – Asteraceae. Cambridge University Press, Cambridge: XXVIII + 624 p.

Wann J.D. (2000) Verbena. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 151-153.

Sell P. & Murrell G. (2006) Flora of Great Britain and Ireland. Vol. 4 Campanulaceae – Asteraceae. Cambridge University Press, Cambridge: XXVIII + 624 p.


Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith