Bird-in-a-bush and least yellow-sorrel

Yesterday we had a family visit to some friends who live north of Boston, and on the way we dropped in at Kirton to do a very quick session of botanical recording. I'd had a look at the existing records and ascertained that there was only one post-2000 record for the tetrad, so the data would be useful. I'd also noted that there were a couple of records for bird-in-a-bush Corydalis solida, a species I'd never seen naturalised, though we have it in the garden.

As usual we headed to the churchyard first, and I was amazed to see prolific quantities of this species growing in a shady area under a row of Tilia x europaea and Aesculus hippocastanum. It is very distinctive, having beautiful purple flowers and lobed bracts. There are few records for Lincolnshire, although it does seem to have turned up more frequently in churchyards than its other habitats, which can include woods and hedges.

 The other exciting species for me was least yellow-sorrel Oxalis exilis, which was flowering on the wall around the churchyard, and was also locally abundant at the base of the church. It is quite similar to procumbent yellow-sorrel Oxalis corniculata, which is a major weed in my garden, but it never has purple foliage. Additionally the inflorescence is always one-flowered and only five stamens have anthers, whereas all ten stamens of O.corniculata have anthers. It's a native of New Zealand and Tasmania, and in South Lincolnshire seems to be more frequently recorded in fen towns than in other parts of the vice-county.

Sex in the churchyard

After a morning meeting in Sleaford, I spent the rest of the day botanising in three Lincolnshire villages, which tend to be oases in the rather intensively arable landscape of huge wheat fields and scrappy, over-managed Enclosure Act hedges of much of south Lincolnshire.

I always make a bee-line for the churchyard, as this often contains fragments of species-rich grassland or woodland species such as primroses and violets.  The churchyards at Silk Willoughby and Osbournby rewarded me with a reasonable suite of species, but at Aswarby I was met with close-mown improved grassland, devoid of any interest.

The churchyard at Silk Willoughby had a very impressive range of primroses. Many were the native type (Primula vulgaris subsp. vulgaris) with soft yellow flowers, but there were also a significant number of clear pink specimens, with a white band round the yellow centre,  which I suspect are P.vulgaris subsp. sibthorpii. This subspecies becomes more frequent from Greece eastwards . It has been cultivated, it seems, since the early seventeenth century, when it was known as 'Tradescant's Turkie-Purple Primrose'. It is assumed to be one of the sources of different colours in garden primroses. 

Certainly primroses are a promiscuous bunch, and have been busily cross-pollinating with gay abandon, giving rise to flowers of many different shades of pink. There also seems to be some evidence of the influence of garden polyanthus around, as a number of the plants had multiple blooms on a single stem. 

Osbournby churchyard had an impressive number of sweet violets, with three distinct varieties present: the deep purple var. odorata, the white var. dumetorum and the attractive pinkish-purple var. subcarnea, which seems to be relatively uncommon locally.

Tallington Teasers

On Sunday I spent a couple of hours recording around Tallington village, in TF00Y and TF00Z. The weather was perfect, and many of the spring ephemeral species were in full bloom, particularly Erophila verna, which seems to be having a bumper year. 

One of the more puzzling pairs of white Brassicaceae are hairy bittercress Cardamine hirsuta and wavy bitter-cress Cardamine flexuosa. The most reliable character to separate this species pair is the number of stamens, which is normally four in C.hirsuta and six in C.flexuosa. However, sometimes these can be hard to see, even with a good hand lens. The habitat gives a good indication - C.hirsuta is usually in open and cultivated ground, on rocks, walls and pavements, and can be a major garden weed. C.flexuosa is usually in more shaded and damper areas, particularly in marshes and streamsides, and tends to look noticeably taller and lusher. At Tallington, C.hirsuta was frequent, but I found one small population of C.flexuosa along the banks of the River Welland.

Cardamine flexuosa showing the six stamens

The hedgerows were brightened by lesser celandine Ficaria verna and locally abundant sweet violet Viola odorata, which was present in several colour forms. Most were the characteristic bluish-purple of V.odorata var. odorata, but there were some populations of V.odorata var. dumetorum, which has a violet-purple spur with whitish petals (sometimes splashed purple) and the lateral petals bearded. You can see a couple of examples below.

V.odorata var. dumetorum, showing purple spur and white petals

Purple-splashed petals with bearded laterals

One of the most interesting species I found was a specimen of intermediate polypody Polypodium interjectum growing on a shaded north-facing limestone wall, together with black spleenwort Asplenium adiantum-nigrum. Polypody ferns are distinctive but can be quite awkward to identify to species, and really require microscopic examination of the sporangia. The only two species which occur in our area are common polypody P.vulgare and intermediate polypody P.interjectum, and both are very local. Their habitat preferences can assist with correct identification: P.interjectum generally prefers more basic substrates including limestone walls and the bark trees such as ash. P.vulgare grows on acidic substrates, including granite walls, non-limestone rock outcrops and as an epiphyte on acid-barked trees such as oak. If in doubt, polypody can be recorded as Polypodium vulgare sens. lat.

Polypodium interjectum on a limestone wall. Note oblong-lanceolate shape of fronds (scarcely parallel-sided).

Blackthorn

After showing Prunus cerasifera in my last post, I thought that I would show the blossom of blackthorn Prunus spinosa for comparison. I think you can see the creamier tone of the flowers, which is accentuated by the almost yellowish buds, golden anthers and complete absence of pink in the middle of the flower. The whole bush is stiffer and more angular, as well as being noticeably spiny, and the clusters of flowers are more separate. It's just coming into flower in sheltered areas around Peterborough, whereas Prunus cerasifera is starting to go over.

The first blossom..

The parkways round Peterborough are swathed with the snowy blossom of cherry-plum Prunus cerasifera, which was widely used in landscaping by the Peterborough Development Corporation.  It's  widely naturalised and may occurs in hedgerows and in scrubby areas. It's easiest to identify at this time of year, as it comes into flower a couple of weeks or so before its close relative, blackthorn Prunus spinosa.

It tends to be taller than blackthorn, growing to 8m and has a more lax appearance. It's never as spiny and the young twigs are hairless and glossy green. Although both have white flowers, I always think that Prunus cerasifera is a purer white, and that blackthorn has a more creamy-tinge, especially when it's young. The other good time to record this species is in the autumn as the fruits of Prunus cerasifera are like small yellow or red plums, compared with the typical sloe of Prunus spinosa.