This photograph isn’t my greatest piece of camera work – sorry. I hope it is recognisable to those who know this wild flower and sufficient for those who are not familiar with it to be able to spot it in future. It is Hawkweed. Botany books give it the name Hieracium umbellatum. This photo was taken on the longest day after weeks of warm/hot dry weather as evidenced by the dried grass in this small meadow area where I live.
A few days before this a larger group of Hawkweed appeared in our garden, in a lawn, now equally dry. It was a relative of that pictured above. It flowered and I thought it attractive. I had planned to take photographs of it but events overtook me. It was Mouse-ear hawkweed Pilosella officinarum. A day or two before we had had the lawn treated for moss (with iron sulphate, no herbicides). The Mouse-ear hawkweed has smooth mat forming leaves, silvery green and untouched by a mower. In fact I was reflecting recently on the weeds growing in our various lawns and they are exclusively low growing and little affected by mowing. To my reckoning this is an interesting example of natural selection at work in a very short time span. Anyway back to the Mouse-ear hawkweed I had been a bit reluctant to manually weed it out as the moss killer was still sitting on the parched plants. (That lawn is now an interesting mix of black areas, dead moss, and brown parched grasses – no hint of green). To continue, my wife – the gardener in our household – asked me to remove the Mouse-ear before the flower heads turned to seed. It was evening when I set about the task but I took my camera fully intending to get the photos of the flowers (not unlike those of the Hawkweed in the picture above) but that patch of lawn was now in shade and the flowers had closed up for the night. So wearing gloves and down on my hands and knees I set about removing the mat of silvery / grey / green rosettes. The patch was about two feet across, or so I thought. Despite the parched grass and soil the Mouse-ear plants came out if tightly grasped and steadily pulled. They came out roots and all, with numerous strong green creeping shoots (stolons, long stems or shoots that arises from the central rosette of a plant and droops to the ground. They may form new plants where they touch the soil). I was thoroughly impressed by the extent, vigour and number of these stolons. They extended, within the grass thatch, beyond the visible mat and would have added to the affected area by creating additional rosettes if it had rained.
As I turned to my favoured botany reference books I discovered that there are many species of Hawkweed around the world. In some countries e.g. New Zealand they are a noxious weed and it is illegal to plant them despite their attractive appearance as in the garden centre offering Fox and cubs.
So along with other low growing species in our lawns, clover, creeping buttercup, creeping cinquefoil and others it was quickly apparent to me that the Mouse-ear hawkweed could happily reproduce with runners without the need for even a casual visit to its pretty yellow flowers by a pollinator.
The rosettes complete with stolons were deposited in our garden waste recycling bin. I assume that they will compost nicely at the waste recycling facility, more likely to be a success than would have been the case had I added them to our garden composter.
So curiosity aroused further by the capabilities of hawkweeds I returned to my botany books and the internet. As with many wild plants, classification is not straight forward and causes much debate among experts. Hawkweeds belong to the daisy family (Asteraceae) and have a more than passing resemblance to dandelions.
Apart from a few named species e.g. the Mouse-ear hawkweed Pilosella officinarum botany books use the name Hieracium agg. Agg meaning a closely related or difficult to distinguish group of plants grouped for convenience as an aggregation.
Hawkweeds, with their 10,000+ recorded species and subspecies, do their part to make Asteraceae the second largest family of flowers.
Botanists around the world researching the Hawkweeds have not reached a consensus on classifying these apparently simple plants. Some references suggest over a 100 or over 200 species and the other plants so subtle in their differences that classification becomes near impossible and of little value to the average observer like me. Nevertheless I cannot deny their great curiosity value.
So why is this so?
Well, innocent little hawkweeds growing in my lawn (Pilosella) and in the meadow down the road (Hieracium) exhibit some unusual properties.
Many members of the genus Pilosella reproduce both by stolons (runners like those of strawberries) and by seeds, whereas true Hieracium species reproduce only by seeds. In Pilosella, many individual plants are capable of forming both normal sexual and asexual (apomictic) seeds, whereas individual plants of Hieracium only produce one kind of seed.
So what if there are no pollinators around? This has been the case I am sure in this prolonged very dry weather I doubt that the hawkweeds have had enough moisture to spend making nectar, so no interest to pollinators. In any case I was instructed to remove the plants before they seeded.
Pollination leading to sexual reproduction may occur. If not sufficient then run out some stolons. Better yet, there is the capability that has evolved in Pilosella to reproduce by seed but asexually. Effectively this is self-cloning. Hence the large number of slightly different members of the aggregation.
If this self-cloning continues then the small differentiating factors which make it difficult for botanists to agree on how many species of hawkweed exist may themselves become established through natural selection and eventually lead to new true species.
Insect pollination is vital for the continuation of many flowering plant species but ironically it can be the absence of pollination which may lead to the evolution of new species.
I hope you share my excitement about the wonder and mysteries of nature, not least the little yellow flowered daisy like treasures that pop up in a moss infested, desiccated lawn.