Parasitic plants in Teesdale

While doing a session on eyebrights in Widdybank Meadows with Margaret’s botany group on monday, we were pleased to see semi-parasitic plants from four different genera (Euphrasia, Rhinanthus, Pedicularis and Bartsia) in the very species-rich flush in one of the meadows.

Marsh lousewort Pedicularis palustris always grows in good quality wet habitats, so when you spot it, there is always a good chance that you will find other interesting plants with it.

The picture below is of the common subspecies of yellow rattle Rhinanthus minor subsp. minor, but at Widdybank Meadows, we also get the much rarer upland subspecies monticola, with tapering leaves and a brownish flower.

We get six species of eyebright in Teesdale: E. arctica, E. confusa, E. nemorosa, E. scottica, E. micrantha and E. officinalis subsp. monticola. And, of course we probably get just about every possible hybrid combination between this set of species. In our flush, the eyebright looked a bit like Scottish eyebright E. scottica, as you would expect in that habitat, but it had largish flowers with a long lower lip and leaves that were not as narrow as you would expect typical E. scottica leaves should be. My guess was that it may have been the hybrid between E. scottica and arctic eyebright E. arctica, which is abundant in the adjacent meadow vegetation.

The photo above is of montane eyebright E. officinalis subsp. monticola. This is one of our special rare plants and one of my favourites. It only grows in species-rich upland hay meadow vegetation and mostly in the rarest form of damp upland hay meadow vegetation (M26b in the NVC classification). It is a Nationally Scarce species and listed as Vulnerable on the UK Red List. There was a small population of it in one of the other meadows at Widdybank Farm on monday night.

The fourth semi-parastic plant we saw in the flush was alpine bartsia Bartsia alpina, which was looking really good and even had flowers! This is another of the Teesdale special plants. It is Nationally Rare, with it’s main British distribution in the Breadalbanes in Scotland. It is very rare in England and is listed as Vulnerable on the England Red List.

Species in all of these genera are considered semi-parasitic, because they are parasitic on the roots of other species, but they also have chlorophyll, so they don’t rely totally on their host plants. Broomrapes Orbanche and Parentuciellia species, and toothworts Lathraea species, are totally parastic and have no green parts. In Teesdale I don’t think we have any records of broomrapes, but we do have a few for toothwort Lathraea squamaria.

Both the semi-parasitic and totally parasitic genera are now in their own family Orobanchaceae, following recent DNA work. Before, the semi-parasitic genera were included in a very variable Scropulariaceae family. The other genera that were included in Scropulariaceae in the past have been further split into a much smaller Scrophulariaceae (which now includes genera like Scrophularia, Verbascum, and bizarrely, Buddleja), the new family Veronicacea (including genera like Veronica, Digitalis, Cymbalaria, Kickxia, Linaria and Erinus) and several other new families, none of which include any native British species. This new arrangement seems to make sense. This is reassuring, as keeping up with taxonomic changes can be annoying and might seem pointless, but changes like this seem worthwhile.

The new Orobanchaceae family includes several other geenra of semi-parasitic plants. In Teesdale we have a few records for red bartsia Odontites vernus, but it is much more common in the lowlands.

We get quite a bit of common cow-wheat Melampyrum pratense in the more wooded parts of the Tees riverbank. There are old records for the much rarer small cow-wheat Melampyrum sylvaticum from a few places places along the Tees, but the most recent record we have is from 1976. We would love to find some of this again. It is one of those species that is often recorded in error, as less experienced botanists sometimes assume they have found it when they find small plants of common cow-wheat. Unfortunately, it is not that simple!

Also, one of the characters given for identifying it is difficult to interpret. For M. sylvaticum, the lower lip of the corolla should be strongly reflexed, while in M. pratense it is ‘not reflexed’, with it’s underside forming a straight line with the corolla tube. However, in the photo above, you could be tempted to go for a reflexed lower lip, as a small portion of the end of the lower lip is clearly reflexed. But the whole lower lip needs to be turned down and not forming a straight line with the corolla tube.

A less confusing character for separating them is in the calyx. If you look at the calyx of the lower of the two flowers in the middle of the photo above, you can see that the lower two calyx teeth are appressed to the corolla tube. In M. sylvaticum these would be patent, i.e. sticking out at right angles.

Small cow-wheat is Nationally Scarce (and very close to being Nationally Rare), with all of it’s more recent British records from Scotland. It is listed as Regionally Extinct on the England Red List. Please look out for this species if you are walking along the Tees riverbank! And don’t forget to let us know if you find it!