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Two plants surviving on the pavement edge

Two plants surviving on the pavement edge

In the last post I used Poland and Clement to successfully identify the plant on the right side of the sketchbook as Senecio vulgaris.

With the plant on the left hand page I went through the same process (Key to major Divisions) but failed because I incorrectly assumed the leaves to be compound (composed of leaflets) when in fact the leaflets are not distinct but joined by thin sections of leaf on either side of the stem, so they are in fact simple.

Second time around having decided the leaves are simple, the most difficult part is to ensure you are reading the correct part indentations of the key. The next stage is to decide whether the leaves are toothed (but not lobed) or lobed (often toothed). Presuming the latter then the Division is P (same as S vulgaris).

Once in Division P the process is again fairly straightforward, though it does rely on deciding whether latex is present or not. I ended up cutting across the main stem to properly see the latex in my plant.

‘Latex is simply a coloured juice which exudes from broken canals or lactifers within the plant tissues. Latex is usually white (at least initially) and is often present only in the young tissues of a plant. A cross section of young petioles (and rootlets) is a good means of locating latex although it can still be sparse and easily overlooked…’ (Poland and Clement, p 492)

Once the latex is detected the next stage is a careful look at the hairs, and the description of hairs and accompanying illustrations in this book are outstanding. It prompted me to look again at the hairs on the edges of the leaves which are slightly downward pointing and sharp tipped (but not prickly to touch).

Anyway Group PF is mainly Lettuce (Lactuca), Sow thistles (Sonchus)and Astrantia. There is much mention of stems in this part of the key and as I’m looking at mainly leaves in a basal rosette its difficult to be sure whether these characters apply. There are also some good words like moniliform (hairs like string of beads) and runcinate (with lobes directed backwards to leaf base). So taken together I think I can say with some confidence that the plant is Smooth Sow-thistle Sonchus oleraceus

In conclusion I think that this is a very useful book. I have tested it on two plants occupying the same habitat and from the same family, the Asteraceae. What is interesting is seeing just how similar they are, both having rosettes of leaves and cottony hairs when young, indeed both have moniliform hairs. The individual leaves are also lobed, not compound and the stem cross sections are similar but there are noticeable differences in the pattern of leaf veins. The presence or absence of latex is very important and time needs to be spent to ensure that it is not present.

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