Plant of the Week, 10th April 2023 – Meadow Saxifrage – Saxifraga granulata

 Saxifraga granulata by the Swedish botanist C. A. M. Lindman (1856–1928), taken from Bilder ur Nordens Flora (first edition published 1901–1905).

I’ve walked along the old road at Bennane Head in Ayrshire many times and there is always something new to spot. Three weeks ago I saw a group of tiny white flowers which turned out to be the Meadow Saxifrage, Saxifraga granulata. I wasn’t sure at first, as this is not a meadow and the species normally grows taller. The plants were just a few centimetres tall, growing on a rocky knoll at the base of a cliff, very close to the road. It’s not a real road anymore, but an abandoned section of the A77, left to go wild when the new section of A77 was opened in the early 1990s. The old road surface is still there, open to walkers who may wish to explore the seascape and admire the view of Ailsa Craig and the Mull of Kintyre.

Saxifraga granulata in full flower. Note: hairs all over, several flowers per stem, leaves are mostly at the base, forming a rosette. Petals are ~1 cm long. Photo: John Grace.

I found three colonies of these plants and I was excited. Back home, having checked the identification,  I discovered that BSBI Recorders had seen it several years before me. Moreover, Saxifraga granulata was already noted as one of the species in the description of the Bennane Head as a Site of Special Scientific Interest. When I returned last week the plants were in full flower, and mature flower-stalks had extended to nearly 10 cm.

S. granulata, early stage late March 2023. Note: stem not yet elongated, red tinge, flowers pure white. Photo: John Grace.

Meadow Saxifrage is a native perennial plant first mentioned in 1568 by William Turner,  the ‘Father of English Botany’ and described in Gerard’s Herbal of 1597 under the old name of White Saxifrage. Evidently, in those days it was a common plant in the south of Britain and especially around London. Gerard said:

 “The white Saxifrage groweth plentifully in sundry places of England, and especially in a field on the left hand of the highway, as you go from the place of execution called Saint Thomas Waterings unto Deptford by London. It groweth also in the great field by Islington called the Mantles: also in the green places by the seaside at Lee in Essex, along the rushes, and in sundry other places thereabout, and elsewhere; it also grows in Saint George’s Fields behind Southwark”.

Habitat: a rocky knoll with Stonecrop (Sedum sp.), Wood-sage (Teucrium scorodonia) and Spear Thistle (Cirsium vulgare). There are four clusters of S. granulata in flower. Photo: John Grace.

Another unusual feature of Meadow Saxifrage is the sexuality of the species: some populations are gynodioecious (Stevens and Richards 1985). This is the condition wherein some individuals are fully hermaphrodite, with normal development of male and female parts (stamens with anthers representing the male, and styles with stigmata representing the female)  whilst other individuals have failed to develop the male part (the anthers may be present but with no pollen).  It is the unusual situation which we saw in our blog on Honckenya peploides; in such cases we seem to be witnessing a transition from perfect hermaphrodite flowers to those which are either male or female (i.e. the dioecious condition). Charles Darwin was one of the first to draw attention to the phenomenon; his book on the sexuality of flowers written in 1877 gave several examples. The topic has interested generations of evolutionary biologists since Darwin’s time.

This flower is clearly hermaphrodite with yellow enlarged anthers. The stigmatic surfaces are underdeveloped because the species in protandrous (i.e. the male part develops before the female to prevent self-pollination). Photo: John Grace.

Meadow Saxifrage seems to have been first-recorded much later in Scotland. The earliest record I can find on the BSBI database is by the Reverend J Gorrie in 1890, in the grounds of Galloway House in the extreme SW of Scotland. The site still exists as a seaside garden at Wigtown Bay but the species has not been recorded there since 1890. However, there are modern records within a few km of the Bay, although most of the Scottish records are on the east coast, not the west.

In the lower two flowers the stigmata are enlarged, presumably receptive, and the anthers are shrivelled. One author mentions “large fat papillous stigmas borne on long styles”. The anthers may have discharged their pollen already or possibly these are female (gynodioecious) flowers where the male parts are dysfunctional . Photo: John Grace.

We tend to think of saxifrages as mountain plants but this one grows in lowland areas and ascends to only 458 metres in our uplands. It is one of several saxifrages that can be seen at sea level as pointed out in one of our earlier blogs here. In Britain and Ireland it occurs on base-rich or neutral well-drained soils, often in pastures and meadows (as its English name suggests) and even in flood meadows and sometimes damp woodland. Its traditional habitat of lightly-grazed damp meadow has largely been replaced by intensive agriculture. Meadow saxifrage has been recorded in old graveyards but these days such places are often mown too short for the survival of many of our native species.

The name of the genus, Saxifraga, means ‘stone-breaker’. The ‘stones’ referred to are probably kidney stones. The ‘doctrine of signatures’ accepted by the Ancient Greeks stated that herbs resembling various parts of the body can be used to treat ailments of those body parts. Many Saxifrages have leaves that are roughly kidney-shaped, thus signalling their possible use for treating ailments of the kidney, especially kidney stones.  

Examples of leaves showing: leaf stalk, flower stalk and leaf itself hairy with glandular hairs, leaf stalk longer than leaf, shape of leaf overall kidney-shaped but with marginal lobes. Photos: John Grace.

So what did Gerard say about the value of Meadow Saxifrage as medicine?

“The root of White Saxifrage boiled in wine and drunken, provoketh urine, cleanseth the kidneys and bladder, breaketh the stone, and driveth it forth, and is singular good against the strangury, and all other griefs and imperfections in the reins”.

I think ‘strangury’ refers to difficulty in urinating and ‘reins’ is French and refers to kidneys.

What sort of a plant is it? There are several unusual features. The first is, it has spherical bulbils at the base of its leaves. Gerard refers to them as “small reddish grains or round roots as big as peppercorns”. The grains were sold by apothecaries as Semen Saxifragæ albæ and consumed by people with kidney complaints. They are a form of vegetative reproduction, over-wintering organs, rich in starch, capable of sprouting new plants in the spring. Turner, Gerrard and the Swedish illustrator Carl Axel Magnus Lindeman thought the bulbils were produced along the length of the roots; however, British floras make no mention of this, and my brief search of on-line herbarium specimens from Britain show bulbils only at the base of the leaves, corresponding to the level of the soil. This limited-distance vegetative spread accounts for the clumps of identical plants.

Might the plant exist in two forms, some with root bulbils and other without? This is not so fanciful as it might seem. The species is said to be highly variable and is strange in having a wide range of  chromosome counts: 2n = 52 is common but 2n can also be 30,46,48,49,and 60. What is going on? It is hard to see how such enigmatic counts could arise from polyploidy alone and quite different processes must surely be involved. In other species of Saxafraga there are known to be supernumerary chromosomes which add to the chromosome count but apparently do not contribute to the genome (Soltis 1983). Unfortunately the study of the cytogenetics of plants went out of fashion, eclipsed by the rise of molecular genetics, and the phenomenon of supernumerary chromosomes is still not understood.

The perennial life cycle of Meadow Saxifrage, starting in the early spring seems to be as follows: (i) leaf rosettes expand in early March, (ii) stem extension and flowering in late March and April, (iii) seeds and bulbils are formed July, (iv) the plant dies down in late summer, seeds and bulbils are dispersed perhaps aided by wind and animals, (v) germination and growth of shoots and bulbils occurs in Autumn (vi) over-wintering with leaves close to the ground. This species is new to me, so I’ve gathered this information from several sources including Fay (2009). I’m going to keep an eye on the Bennane population to see if this chronology is correct.

British distribution of Meadow Saxifrage, from BSBI. Note that many squares where the plant was recorded prior to the year 2000 (pale browns) no longer contain the plant, showing a general decline.

I would like to determine the sexuality of the Bennane plants by photographing the individual flowers so that I can classify then as hermaphrodite or female. Photography of small plants growing on windy knolls on steep slopes is not easy, but I’m going to give it a try. My initial impression is that most flowers are hermaphrodite but in a significant fraction of the population the male component is poorly expressed to a variable degree. The situation is not clear-cut. We shall see.

World and distribution of Meadow Saxifrage, from GBIF. It does not stray very much from its home in Europe, unlike many native species we have featured on the blog (which become invasive in other parts of the world).

References

Fay MF et al. (2009). Saxifraga granulata L. (Saxifragaceae). Curtis’s Botanical Magazine 26, 74–85.

Soltis DE (1983). Supernumerary chromosomes in Saxifraga virginiensis (Saxifragaceae). American Journal of Botany 70, 1007-1010.

Stevens DP and Richards AJ (1985). Gynodioecy in Saxifraga granulata L. (Saxifragaceae). Plant Systematics and Evolution 151, 43-54.

John Grace