Knapweed Novelties

Shortly after completion of construction of the A1(M) east of Leeds in 1999, the verges and road junctions in the vicinity of Aberford and Hook Moor (VC64) became briefly notable for unusual flora. Most especially, for the knapweeds that established from the seed mixtures used to 'restore' the affected landscape. Chief amongst these was Panicled Knapweed (Centaurea rhenana), a delicate airy species from mainland Europe. Its had a name change since then and now goes by Centaurea stoebe subsp. stoebe. It only really came onto my radar when Mike Wilcox re-found it in 2019, a remarkable 20 year persistence for a species still not listed in Stace or any other British Flora. 

So finally, I made a conscious decision this weekend to pick an area of promising habitat near the motorway to see if I could find it. And I did. What was even better was that the location I chose to search is a new one. The plot has also recently thickened with Mike advising me that the true identity was likely to be a related subspecies that is widely known as an invasive species in Europe and North America. This is Spotted Knapweed (Centaurea stoebe subsp. micranthos), a species it runs down to nicely in a key I found online.

The verges of the A1(M) between Garforth and Aberford are also a dependable hunting ground for Brown Knapweed (Centaurea jacea), although it is vastly outnumbered by its hybrid with the native Slender Knapweed (Centaurea debeauxii subsp. nemoralis) i.e. Centaurea x monktonii. Based on the situation in West Yorkshire, this hybrid must be widely overlooked elsewhere within the core range of Slender Knapweed. One to look for in modified landscapes where knapweeds have been introduced in the past.

More unexpected after the above was a robust knapweed well off flowering but with well developed buds with feathery recurved phyllaries. This seems to be Centaurea oxylepis, which will have also derived from the original sowing some over 20 years ago.

The final good find was two new locations for an alien Greater Knapweed first found by Mike to the north of Aberford in 2021, which we came to the decision (based on limited online sources) was a good match for Centaurea scabiosa subsp. alpestris. This is a striking species with, when compared with the native subsp. scabiosa, very variably dissected yellow-green leaves, and larger capitula with a much more prominent (but variable, even on the same plant) black apex to the phyllaries.

Townclose Hills SSSI (VC64)

Making the most of sunshine and a day off work I decided to walk over to Kippax and see what I could find at Townclose Hills SSSI, a fabulous remnant of unimproved limestone grassland affording great views over the lower Aire Valley. I wasn't quite sure what I would find, as the season seems to be whipping on at a rapid pace this year, with Butterfly-bush (Buddleja davidii) unbelievably in full bloom at the end of June. Thankfully, recent rain seems to have reinvigorated increasingly stressed flora, and grassland habitats at least are about where they should be for the time of year. Certainly, the grasslands of the SSSI were a carpet of flowers, with plenty to see. Highlights included:

Carpets of the native form of Kidney Vetch (Anthyllis vulneraria subsp. vulneraria), strictly prostrate to prostrate-ascending on weak stems.

Masses of Greater Knapweed (Centaurea scabiosa var. scabiosa), an uncommon plant locally.

Good swathes of Yellow-rattle (Rhinanthus minor subsp. stenophyllus), a subspecies more typical of calcareous fens further south but less fussy in Yorkshire where the local climate is more accommodating.

Perforate St John's-wort (Hypericum perforatum) which many will not consider that exciting, but I'm increasingly of the view that its not that common. I suspect it is widely over-recorded, especially in Yorkshire, for its hybrid Des Etang's St John's-wort (Hypericum x desetangsii). Recorder's shouldn't assume Perforate St John's-wort unless they have not checked the sepals carefully for the absence of teeth. By default it is therefore a plant that should only be named when in flower.

Plenty of Clustered Bellflower (Campanula glomerata) just starting to come into bloom.

With time to indulge this spring, and with an exceptional new BSBI Handbook to accompany Vince Jones' regional monograph (criminally under-printed by the Yorkshire Naturalist's Union), I've been dipping my toe into hawkweeds. One of the commonest locally, and earliest flowering, is Southern Hawkeed (Hieracium argillaceum). There was plenty of this in the grassland on steep slopes.

Moving down slope to the wooded margins of the SSSI provided:

Orange Whitebeam (Sorbus croceocarpa)

The largely sterile hybrid between Dewberry (Rubus caesius) and Raspberry (Rubus idaeus) i.e. Rubus x pseudoidaeus.

And, surprisingly, a highly scented hybrid Mock-orange (Philadelphus Lemoinei Group).

Into the woodland proper was a welcome plant of Soft Shield-fern (Polystichum setiferum), an uncommon species in the lowlands to the east of Leeds but one which is increasingly being found in small numbers in woodland habitats.

Great Staughton Churchyard

In stark contrast to most of Huntingdonshire's overly manicured churchyards, the churchyard at Great Staughton (or at least the part on the north side of the road)  is gloriously neglected and alive with flowers and insects.

The churchyard is notable for its swathes of Wild Marjoram (Origanum vulgare). This is a rare species in the county and is probably introduced at this location. This is supported by the diversity of forms present, some have the dense inflorescences, deep rose pink flowers and vividly purple bracts of the true wild form, while others have white or pale pink flowers, pale bracts and a much laxer inflorescence.

The churchyard also provided the great surprise of Des Etangs' St John's-wort (Hypericum x desetangsii nothosubsp. desetangsii) a species not previously recorded for the county. We shall have to start scrutinising our Perforate St John's-wort (Hypericum perforatum) a little more closely going forward, so check the sepals with a hand lens for small teeth.

The churchyard also had a nice colony of Field Scabious (Knautia arvensis) and a swathe of Common Knapweed (Centaurea nigra agg.). Much of it looked like a hybrid swarm, with flowers strongly resembling true C. nigra but much too small and with phyllaries variable in shape. A few plants resembled true Chalk Knapweed (Centaurea debeauxii) which is common on drier soils throughout the county, and given this species flowers slightly later this may help it stay true to type as it is still in bloom after true C. nigra has gone over.

The nearby River Kym was also looking good with abundant Arrowhead (Sagittaria sagittifolia), Yellow Waterlily (Nuphar lutea) and Common Club-rush (Schoenoplectus lacustris).

This little gem was on the bridge over the river - white flowered Hedgerow Crane's-bill (Geranium pyrenaicum f. albiflorum) which comes true from seed and had established a small colony.

St Aidan's Part II

There is much more to St Aidan's than obscure species of rush! The wetland habitats are extensive and surrounded by grasslands that are in peak bloom at the moment.

One of the most prominent species currently in flower is Chalk Knapweed (Centaurea debeauxii) which is not uncommon on the lighter soils to the east of Leeds, but the plants here undoubtedly came in with the seed mix that was sown over most of the site during restoration of the former colliery.

The grasslands also support a range of legumes, including several robust fodder forms of native British species such as Bird's-foot-trefoil (Lotus corniculatus var. sativus), Red Clover (Trifolium pratense var. sativum), and White Clover (Trifolium repens var. grandiflorum). There were also several large monospecific stands of a very large form of Spotted Medick (Medicago arabica), again probably a fodder selection. The Medick had gone to seed and was smothered in its characteristic coiled seed pods.

Another native legume present was Zigzag clover (Trifolium medium) with its large bright pink flowers and distinctive elongated leaflets.

I wasn't the only one enjoying the flowers.