Paul's Back Garden Safari

Toothwort – Lathraea squamaria (Orobanchaceae)

This is a strange one. A fully parasitic plant, there are not many of them around, and even fewer that occur in the UK. The Toothwort, Lathraea squamaria is one such. The common name relates to the tooth-like scales that are found on the it’s rhizomes, which according to the Doctrine of Signatures was considered to be good for teeth. This is the only reference to any medicinal use that I can find, which when we consider the usual life cycle is unusual. But then everything about the Toothwort is unusual.

The first time I came across this plant was along an ancient hedgerow trackway. But I stumbled across it again this week, also in a green lane bounded by an old hedgerow. This time it was growing at the base of the stump of a felled deciduous tree, no idea what it was, but there was plenty of hazel very close by. It is most commonly found parasitising hazel (Corylus), but can also be found on other plants including elm (Ulmus), ash (Fraxinus), alder (Alnus), walnut (Juglans) and beech (Fagus).

The Toothwort is lacking completely in chlorophyll, no part of the plant is green. This lack of chlorophyll means that Toothwort is unable to photosynthesise and to meet its own energy needs, and therefore depends upon the parasitic relationship the individual plants create with the host. The pale pink and slightly ghostly flowers appear in April and May, and this the only time of year you’ll have any chance of seeing it. The ghostly appearance of the Toothwort led to its other vernacular name of Corpse Flower.

The majority of the toothwort is remains invisible throughout the year, existing as a white fleshy rhizome underground. The rhizome itself is covered by four rows of white scales, which are in fact the plant’s leaves, but they remain underground. Each of these modified leaves contain a central chamber (lacuna), which is lined with dome-shaped glands. It is thought the lacunae may enable the plants to regulate its fluid content and excrete excess water. Plants have stomata on their leaves, minute pores in the surface of leaves or stems, which allow them to regulate the exchange of gasses and fluid. However, the Toothwort does have stomata and so needs another way of regulating its fluid status.

Toothwort are found in moist and shady places including deciduous woodland, hedgerows, and river and stream banks, but the presence of trees are essential. In order to survive the Toothwort can only obtain it’s nutrients by attaching specialised pad-like structures, haustoria, found on the tips of its roots to the root system of the host tree. The haustorium penetrates the tissues of the host root system to form a vascular union to allow the redirection of nutrients away from the host and into the Toothwort.

Reproduction like everything else about the Toothwort is unusual and varied. The flowers appear at the base of the host plant, and reach a height of between 20-25cm. The colour ranges from white or creamy to pinkish-purple and are produced on drooping, one-sided flower spikes. The flowers themselves are two-lipped with a style (female part) that extends beyond the petals and are pollinated by bumble-bees. However, the Toothwort can also reproduce through developing cleistogamic underground flowers which fertilise themselves. Cleistogamy is a type of automatic self-pollination of unopened flowers that has evolved among some plants families. This method of reproduction is well known in peanuts, peas, and pansy.

Toothwort – Lathraea squamaria was originally included in the family Orobanchaceae, along with other semiparastic plants. Developments in genetics allowed the boffins to reallocate the Toothwort to different families river the years, but it has now found its way back the newly defined and enlarged family of Orobanchaceae. The family now contains both full parasites and semi-parasites including eyebrights, bartsias, cow-wheats and louseworts as well as yellow rattles. All too much fro my little brain. The boffins often claim that the binomial names are the correct and consistent method of classification. However, the more I look at these things the more it seems recent changes in names and in taxonomy, the most consistent classification is in fact the vernacular names. Plus the fact these are the ones I can remember.

So that leads to the etymology of Lathraea squamaria. Lathraea comes from the Greek “lathraios” meaning hidden, and relates to it’s underground existence and lack of presence throughout the majority of the year. Squamaria, come from Latin “squama”, meaning scale. Incidentally, the family name, Orobanchaceae, is derived from the Greek “orbos” and “anchos”, meaning ‘vetch’ and ‘to strangle’, referring to the parasitic nature of the plants within this family of fascinating plants.

I have to admit I was expecting to discover far more about the mythology associated with such a fascinating plant, but there is a real paucity of folklore attached to the Corpse Flower, and very little beyond ‘it might be useful for teeth’ according to the Doctrine of Signatures. But in the end that doesn’t distract from the fascinating life cycle of a parasitic plant.