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Arctium taxa - taxonomic issues re. verification

Posted: Mon Dec 16, 2019 11:00 pm
by AndyAmphlett
For info, and re. verification of Arctium records

The current taxonomy of Arctium (Stace 3rd edition, 2010 and 4th edition, 2019) includes the following taxa:

Arctium lappa
Arctium lappa x minus = A. x nothum
Arctium minus
A. minus subsp. minus
A. minus subsp. pubens
Arctium nemorosum
Arctium tomentosum
Arctium tomentosum x lappa = A. x ambiguum

The first treatment of the genus compatible with current taxonomy was that in Clapham et al (2nd edition, 1962), though in this work A. nemorosum was treated as a subsp. of A. minus. Arctium nemorosum was first distinguished at species level in the 2nd edition of Stace (1997).

NB 1. Old Floras listed all taxa under the name A. lappa. This taxonomic approach was followed as recently as Bentham & Hooker (7th edition) published in 1924, and reprinted up to 1947.

NB 2. There is additional discussion in Plant Crib (1998) - ... m_Crib.pdf

NB 3. Sell and Murrell (2006) adopt an entirely different taxonomy to that adopted by Stace, with all taxa (apart from A. tomentosum) listed as subspecies of A. lappa. They do not included any hybrids in their treatment.

NB 4. A. minus s.l. includes Arctium minus, A. minus subsp. minus, A. minus subsp. pubens and Arctium nemorosum.

Sell and Murrell give distributions of the native & archaeophyte taxa as follows (using current Stace names):

A. lappa - south & central Britain (absent from the north and much of the west).

A. minus subsp. minus - south-west, central & south Britain, the Channel Islands, central & southern Ireland. Absent from Scotland, north of England, and north Ireland.

A. minus subsp. pubens - central & southern Britain, a few records in Ireland & further north.

A. nemorosum - the only taxon in much of north & west Britain & north Ireland. Absent from SW Britain. It overlaps with A. minus subsp. minus in SE England & in a belt from north & west Wales to Lincolnshire & Yorkshire.

As a result of taxonomic changes and (to a degree) difficulty in distinguishing the taxa, there are substantial errors in current mapping of the distribution of A. lappa and A. minus. Such errors may also have been compounded by additional errors where agg. taxa were unintentionally reinterpreted as the s.s. taxon when records were imported into a database.

The distribution map for A. lappa - ... cd4p9h.xba - shows many pre-2000 records to the west and north of the species current core range. Old records, eg some in Scotland are likely to reflect past usage of the name A. lappa to refer to all Arctium species. The records from Cardiganshire (vc46) for A. lappa refer to records using Sell & Murrell's taxonomy. In his Flora for the vc, Chater only gives a single record for A. lappa s.s. (ie sensu Stace), hence all the other records should be mapped as A. minus s.l.. I don't know anything about the situation in SW England, but the occurrence of many pre-2000 (some old) records of A. lappa there (with no more recent records) suggests that there might have been some taxonomic confusion. Worth checking anyway.

The distribution map for A. minus s.s. - ... cd4p9h.m9e - is very similar to that for A. minus s.l.. Given the broad distribution given by Sell & Murrell (and in other Floras), the map appears to be very inaccurate, with many records for the s.s. taxon probably referring to the s.l. taxon. If Sell & Murrell's assessment of distribution is correct, then many (most?) records from Scotland, north of England, and the north of Ireland are incorrect, or suspect, and should be referred to A. minus s.l..

The distribution map for A. nemorosum - ... p9h.1qza6p - shows many hectads in lowland England and in Wales with only old records (many pre-1970). Martin Rand has recently published a note on this species in hampshire: Wood Burdock (Arctium nemorosum Lej.) – does it actually exist in Hampshire? - ... 202019.pdf Further investigation and clarification of records from parts of lowland England and Wales may well be worthwhile.

EDIT Added 17/12/2019. Michael Braithwaite undertook a thorough study of Arctium in vc81. Braithwaite, M. (2005). Arctium - has Stace got it wrong? BSBI News 98, pp.23-25. He concluded that "The treatment of Arctium by Perring, as adopted by Stace in his first edition of his New Flora of the British Isles is supported. The treatment by Stace in his second edition, following Duistermaat, is not supported. The Berwickshire plants examined in this small study are considered to belong to A. minus subsp. nemorosum, sensu Perring except for one population of a local variant that is intermediate between subsp. nemorosum and subsp. minus".

In north Scotland, I tend to records plants as A. minus s.l., though I suspect all are A. nemorosum. In the vcs I am most familiar with, there are no records of A. minus s.s. from vc94 or from vc96. In vc95, McCallum Webster in her Flora (published 1978) only listed a single record of A. minus s.s. (from a distillery tip, where it was introduced); all other records being of A. nemorosum. Ian Green (VCR) considers it likely that all more recent records in vc95 are of A. nemorosum.

I am sure there will be VCRs who have looked carefully at Arctium taxa in their vcs and come to conclusions as to which taxa occur. Editing existing records, in MapMate and the DDb, should be done with care, always trying to accurately reflect the likely intentions of the original recorders. In areas well outwith the core range of A. lappa and A. minus s.s., transferring records to A. minus s.l. (with an explanation) may be appropriate. If in doubt, please discuss with the relevant Country Officer. Unfortunately, it is unlikely that accurate distribution maps of the native & archaeophyte Arctium taxa can be produced, because of past confusions as outlined above. However, there is scope for clarification, without introducing new errors.