Academic ecologists these days spend a lot of time thinking about invasive species: How fast are they likely to spread? What traits allow a certain species to succeed where others fail? What is the impact on native plant and animal communities? With our warming climate, alien species, previously innocuous, might escape from ‘captivity’. Garden plants are of course one of the most common sources. The charity Plantlife recently compiled a list of the plant species most likely to become invasive in the UK in the near future.
Particularly high risk were two tree species, the Tree-of-heaven (Ailanthus altissima) and the False-acacia (Robinia pseudoacacia). The Tree-of-heaven has already spread itself all over London, and seems a good bet to do the same thing in other UK cities in the near future. Both these trees can be found occasionally in Sheffield’s gardens, parks and streets; unfortunately, both produce fertile seed in Britain, and also sucker. Indeed, one of the main problems with these trees in other countries has been their ability to sucker into native woods, potentially transforming them into monocultures. False-acacia suckers particularly can travel considerable distances: the next time you walk past the University Arms pub, up Brook Hill, have a look at the trees at the corner with Hounsfield Rd and you might be able to spot False-acacia shoots popping up at some distance from the main tree. The Tree-of-heaven suckers profusely when the main bole is cut down; the resulting thickets can be seen in some gardens around Sheffield, at the corner of Carr Rd and South Rd in Walkley, for example.
For naturalists keen to monitor potentially harmful changes to our region's flora, the seedlings of these species will be particularly important to keep one's eyes open for.
Thursday, 25 August 2011
I spent the weekend in the Cotswolds with my wife and a friend, and this was one of the botanical highlights, Bean Broomrape (Orobanche crenata). It's not native to Britain, and is currently thought to be naturalised only a one site in north Essex. It does turn up in other southern counties however, as here in Gloucestershire. As you might guess from the name, it parasitises legumes (plants related to peas). This specimen, and the hundreds of other plants in the field, was parasitising White Clover (Trifolium repens). No doubt it was a seed contaminant that arrived with the Clover when it was sown.
The corolla with its five flared lobes (2 up, 3 down), each at almost 90 degrees to the main corolla tube, is a key feature apparently. Although on older flowers this was not so obvious.
Unfortunately this Orobanche is not included in a lot of the popular picture guides to Britain's plants, so hopefully it won't increase too much in Britain: if it does we may not notice! (And it might become an agricultural pest of other cultivated legumes, as it is in North Africa and other warmer climes).
Sunday, 14 August 2011
This is Red Bartsia, or Odontites vernus, growing at the edge of a path in Crookes Recreation Ground, Sheffield. It's not unusual to find it on waste ground or trampled path edges, but it is easily overlooked. Like all members of the Orobanchaceae it is parasitic; in this case on the roots of grasses I believe. It's green, so obviously it can still photosynthesize, so we might suspect it is only using its hosts for mineral nutrients and water. However, the line between hemi-parasitism (as here) and holo- or complete parasitism seems to be fairly thin in an evolutionary sense, so it's possible that some sugars are received from the host as well.
A nice plant to look out for in urban situations; I used to see it a lot in Birmingham along the canal in the Edgbaston area.
Thursday, 9 June 2011
With Remarkable Creatures Sean Carroll, the evolutionary-developmental biologist, expands his already impressive popular science oeuvre. His latest book features 13 sketches of some of the greatest discoveries in evolutionary biology, but also an inspirational appreciation of the creative, smart, often lucky, but always supremely dedicated scientists behind the textbook facts.
Starting, as a prelude, with the great polymath Alexander von Humboldt’s achievements, and his influence on Darwin, Wallace, and Bates, Carroll divides the rest of the book into 3 sections dealing with different aspects of evolutionary origins: the theory of species’ origins; the actual origins of various animal taxa; and the origins of humans. Chances are you will have met some of the scientists, and their discoveries, before; the trinity mentioned above, of course; Louis Leakey, quite possibly; others might ring vague bells, but due to the breadth of the discoveries covered, revelations are guaranteed. The tenacity and daring of Eugene Dubois, discoverer of Homo erectus, and the part played by Linus Pauling in the development of molecular clock theory, were two such revelations for me.
This anthology, of biography melded with discovery, succeeds in finding a wonderful balance between human drama and scientific fact. The excellent referencing and clear scientific content also make it a great introduction to the evolutionary topics covered. Give this book to young scientists whom you wish to inspire; it’s just the antidote for a textbook!
Monday, 16 May 2011
Don’t get too excited folks, I just mean before the flowers come out! Incidentally, the word gamete (sex-cell) actually comes from the Ancient Greek for husband and wife.
Identifying plants without flowers is known as vegetative identification and is extremely useful if you want to identify all the plants (above-ground!) at a site in one visit. The wonderful thing about learning vegetative identification is that it makes one look very closely at a plant. One may start botany by identifying the showier herbs and most obvious trees, but, for an intimate knowledge of plants and how to identify them using keys, training your hand-lens on cilia or hydathodes is where it’s at. Luckily a Vegetative Key to the British Flora (J. Poland & E. Clement; known as ’Poland’) has recently been published, and is available on Amazon.
As an example of the benefits of such knowledge, a recent walk in the Rivelin Valley (Sheffield) to see that “loveliest of trees”, the cherry, yielded the flouncy white flowering spikes of the Bird Cherry (Prunus padus). Even without flowers this can be quickly separated from almost every other Prunus except Rum Cherry (Prunus serotina) by the strongly smelling pith of the twigs (a useful winter ID trick). The heart-shaped (cordate) leaf bases allow us to decide between these two on Bird Cherry: few other books besides the Vegetative Key give you this information.
However, vegetative characters may not solve all of our problems, elsewhere in the valley I encountered a sapling of a Whitebeam (Sorbus spp.) and a large Cotoneaster shrub. Whitebeams and Cotoneasters are both members of that prudish coterie of plants that often go without sex; one of the upshots of this is that clonal reproduction may result in numerous ‘micro’-species with few obvious differences to help the field botanist. This is where we will want to confirm our identifications by taking so-called ‘voucher’ specimens. Understandably, an identification in a database of a difficult plant species that is not backed up by a voucher will likely be discarded by future botanists as unreliable.
The Botanical Society of the British Isles (www.bsbi.org.uk) is there to help botanists in this respect: their network of referees (including a ‘Beginner’s referee’) will check member’s specimens, confirming or questioning their identity. The wonderful thing about botany today is the amount of excellent material and support that is available to the enthusiastic. So, to paraphrase (or butcher!) Housman: since fifty springs are little room, to learn about the things in bloom, I’ll go with Poland and a press, so next year I won’t have to guess.