Sam J. Thomas Nature: X Agropogon robinsonii & others, National Botanic Garden of Wales

A visit to the gardens during last week's heatwave roved productive with a couple of cudweeds, a spurge and a intergeneric grass hybrid.

Polypogon viridis is now among the most common grasses around the propagation glasshouses at the gardens. Reasoning that this increased my chances, I set to hunting for its intergeneric hybrid with Agrostis stolonifera: X Agropogon robinsonii. Despite somewhat conflicting literature including what appears to be an erroneous description in Sell & Murrell I managed to find a single putative hybrid plant. Examination back home under the microscope showed a mixture of characters of the two parent species and intermediate character states. The anther length (c. 1.1mm) being closer to A. stolonifera and much longer than that of P. viridis (c. 0.6mm). The lemma and palea resembling those of P. viridis both in shape and relative length (almost equal). The glumes having sparse scrabidity from P. viridis but more pronounced bristles on the keel from A. stolonifera. The end of the ligule being ciliolate as in P. viridis but the overall structure of the tiller more like that of A. stolonifera. Given these features I'm happy to call the plant X Agropogon robinsonii though it will probably need to be sent off for confirmation. As far as I can tell this hybrid has previously only been recorded four times in the UK (all but one in the Channel Islands) and once in France. Given the rapid spread of P. viridis in recent years it may be that other people have found this hybrid recently. If not it is probably worth keeping an eye out for wherever P. viridis occurs.

***Note*** Now 'cautiously confirmed' by Tom Cope at Kew as the fifth ever record of this taxon. The 'cautious' prefix having to do with some previously confirmed material of this this taxon having been redetermined as pure Polypogon and the fact that the only other available material (a Guernsey collection from 1997 by Rachel Rabey) is much larger and more distinctly intermediate between the parent taxa than NBGW material. On balance however the male sterility and persistent glumes were, according to Tom Cope, enough for the 'cautious confirmation'. Confirmation is with thanks to Richard Pryce, Arthur Copping, Tom Cope and Rachel Rabey.

X Agropogon robinsonii, culm,
NBGW, SN 52105 18410

X Agropogon robinsonii, habit,
NBGW, SN 52105 18410

X Agropogon robinsonii, tiller,
NBGW, SN 52105 18410

X Agropogon robinsonii, inflorescence,
NBGW, SN 52105 18410

Now cudweeds, the most interesting of which was a single plant of Gnaphalium luteoalbum growing on gravel between two propagation glasshouses. This species is restricted as a native to a few sites in the south of England and occurs as a scattered casual elsewhere but appears not to have been recorded in Wales post 1930. Despite fairly extensive searching I could not locate any more plants suggesting that this species may have only just arrived at the gardens.

A more frequent cudweed: Filago vulgaris was abundant on on parched ground around the science block. Bringing the cudweed total for my trip to three including the common Gnaphalium uliginosum.

Gnaphalium luteoalbum,
NBGW, SN 52138 18412

Filago vulgaris,
NBGW, SN 51970 18239

Finally a spurge: Euphorbia stricta is very local as a native being restricted to the open ground in woodlands around the southern Welsh borders. At the gardens it grows in abundance behind a single polytunnel. I don't know if it arrived at the site of its own accord as a casual or, more likely, either as a horticultural species or as part of the Garden's Welsh Rare Plants Project.