Thursday, May 3, 2007

Dandelion Taraxacum ( subhuelphersianum ? )

I am an amateur naturalist attempting to identify all the life forms in my garden. Today: the dandelion.

Photo 1 (click on it to enlarge) shows a dandelion I found growing in my garden (at (0.6,0.9) -see here). In an attempt to learn something about dandelions I have been reading the Dandelions of Great Britain and Ireland (A.A. Dudman and A.J. Richards, BSBI Handbook, 1997).

Dudman and Richards' book is a tour-de-force of field botany. According to the authors, no fewer than 235 "species" of dandelion have been recorded in the British Isles. They give painstaking botanical descriptions and illustrative plant-silhouettes of them all and distribution-maps for most.

Why the quotes around species in the last paragraph? Because dandelions are not like most other plants; Dandelions reproduce apomitically (asexually). This means that all the seedlings from a parent plants are identical clones. The authors describe how planting out the seeds from a dandelion in a row will, under identical growing conditions - for example in a tomato "grow bag" - result in a row of identical baby plants, an idea that for some reason appeals to me greatly and is something I'm determined to try at some point.

Although individual dandelions asexually produce clones, over time mutations emerge in the population: hence the 235 dandelion types listed in the book.

So, how do you begin to tell different dandelion strains apart? The answer is by painstaking examination of the features of a given plant: Are the leaves uniformly green, or are they blotched in places?; What colour is the petiole ? (the mid-vein in the leaf) (example colours include green and purplish-red); Is the scape (the flower stalk) smooth or minutely hairy?; What shape are the bracts (the small "leaves" surrounding the flower-head like a collar) ?; What colour are the stripes on the back (see photo 2) of the ligules (the flower 'petals')?; What shape are the leaves?... There are a dozen features to take into account...

Or at least that's the theory!! When it comes to separating dandelions, as the authors themselves admit: "confusion and frustration [lie] ahead: dandelions are difficult!"

The problem is that dandelion features are enormously variable ("plastic"). Take two clones, grow them under different conditions of light, humidity etc. and entirely different plant shapes and features can emerge. The authors recommend that the only really practical way to build up experience of identifying dandelions is to build up a large collection of dried specimens.

Where does this leave the amateur? Frankly, mired in uncertainty! In the case of my dandelion I can confidently say it was not found on a Scottish mountain top, nor are the capitulas (the flower heads) less than 3cm in diameter. Following the key of Dudman and Richards this means my dandelion in a likely member of the "genus" Ruderalia. I struggle however to bring my dandelion down to a specific one of the 120+ Ruderalia "species"; I can find no evidence of pollen on my dandelion, which would make it most likely to be Taraxacum subhuelphersianum - except that the leaves of this plant are described as "distinctly pale, slightly greyish", which mine aren't. I leave you to judge for yourselves.

Two things intrigue me about dandelions:
One - Most plants flower to attract insects for the purpose of cross-pollination ("sex"). As above however, dandelions don't "do sex". Is the capitula (=flower head) a redundant evolutionary relic in dandelions therefore, or does it serve some other purpose?

Two - For the amatuer, a microscope proves enormously handy when it come to identifying moss and fungi. Photos 3 and 4 show my attempt at a microscopal photo of a dandelion seed (achene) and pappus (=the 'feathery' bit on the seed ). Both show a wide array of bumps, hooks and other features. I would love to think that these features are diagnostic and someone out there is busy putting together a key to dandelions based around their features visible under a low power microscope. Very possibly there is nothing in this suggestion. On the other hand, if you're that person do please leave a comment.


dig this chick said...

Henry, Thanks for your post on my blog...what an interesting tidbit you have about dandelions! I adore the concept of your thread. best.

kwhite said...

hi henry im a mature student and i use microscopic images to create my designs can you tell me do you have your own microscope or do you go to a science lab? i usually go to the labs at uni but i was wondering if there is an affordable microscope i could purchase? thanks great images by the way. I have images i have altered of moss and fungi on my blog if you care to check them out. thanks again, karen