Autumn Purples

Common or Black knapweed (Centaurea nigra) or Mínscoth/Mullach dubh in Irish is common on roadside verges, grasslands and wastelands from July to September. (1) Superficially the plant looks like a thistle because of its deep purple flowers and similar flowerhead but on close inspection it will be noticed that it possesses no prickles. 
The dark brown bracts underneath the flower head are very conspicuous.  This is called an involucre.  It is pollinated by lots of butterflies and insects that have long tongues because the nectar source is difficult to reach.

Purple loosestrife (Lythrum salicaria) or Créachtach in Irish is abundant from July to September in damp places such as riverbanks, bog margins, on damp roadside verges and the sides of lakes and streams. (2)  Its whorls of red purple flowers grow on long spikes on stems that can be 100cm high.  It is pollinated by bees and hoverflies and certain beetles eat its leaves and flowers.

Bittersweet or Woody nightshade (Solanum dulcamara) or Fuath gorm in Irish can frequently be seen this month clambering through damp hedgerows. (3a) This plant belongs to the Solanum family and is therefore related to the potato, tomato, aubergine, green pepper, red pepper and the tobacco plant. 

The five petals which make up the corolla are purple, and the protruding yellow part consists of five closely joined stamens which hold the pollen. The berries which result from fertilization change from green to yellow to bright red. (3b;3c) These are poisonous. They are not as poisonous, however, as the black berries on its near relative, Deadly nightshade (Atropa belladonna). Luckily, this plant is rare in Ireland.  It too has purple flowers, but they lack the conspicuous yellow column of fused stamens.