Tuesday, 23 October 2012

Wednesday wildflower: chickweed.

Last week’s wildflower was the annual mouse-ear chickweed (Cerastium glomeratum).  This week’s wildflower is a chickweed that’s not hairy, or at least barely hairy.  Chickweed is also an edible weed.
A thicket of chickweed, Karori.
Like mouse-ear chickweed, Stellaria media has five divided petals, but these are deeply divided so that the flower seems to have ten simple petals.  There are three stigmas instead of five, a clue that the ovary is made up of only three carpels, but in this family there aren’t any partitions inside the ovary.  There are usually 3–5 stamens, but can be as many as 10.  The single line of hairs along the pedicel (flower stalk, below) is a distinctive feature.
Chickweed, Karori.  Both leaf surfaces (upper on left), a flower, and a young fruit.
This is the commonest of the three introduced chickweeds (the others are S. alsine and S. graminea).  There are also five native chickweeds: S. decipiens, S. elatinoides (probably extinct), S. gracilenta, S. parviflora, and S. roughii.
Stellaria decipiens, Garden Stream, Campbell Island
S. decipiens is hard to distinguish reliably from S. parviflora, but is often fleshy.  It’s confined to the subantarctic islands.  This one has no petals, which sometimes happens in S. parviflora too.
Stellaria gracilenta, Canterbury.
S. gracilenta is a common plant in tussock grasslands in North and South Islands.

Stellaria parviflora, Mt Herbert, Banks Peninsula.
S. parviflora is a delicate herb of the forest floor, and common throughout New Zealand.  In the flower above, the petals are the same length as the sepals, although my description in Flora of New Zealand (Webb et al., 1988) says "petals much < sepals or 0".

Stellaria roughii, Cragieburn Range, Canterbury.
S. roughii is a scree-adapted plant.  It has grey fleshy leaves like other unrelated plants in this harsh habitat.
We don't know yet whether these native Stellarias are all related closely to each other and derived from a single introduction, or whether they represent multiple introductions.


Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. 1988.  Flora of New Zealand Vol. 4.  DSIR, Christchurch.

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