Marigolds, Yellow Chamomiles & Allies
What are they?
Marigolds and related plants form a group of often showy, yellow- or orange-flowered members of the daisy and dandelion family - the Asteraceae. Their flowers differ from those of the dandelions in having strap-like petals or 'rays' around the outside of the compound flowerhead only, with the small florets in the centre being petalless and forming a button-like middle. These plants are annuals or herbaceous perennials and are often grown in gardens for their showy flowers, which can be produced throughout the summer. The plants tend to be multistemmed, while the flowerheads are mostly carried singly on long stems.
Where are they found?
Most are plants that are grown ornamentally and are most likely to be found as garden escapes or throw-outs on roadsides, waste ground or other grassy places. Corn Marigold is a weed of arable margins.
Identification
The flowers of this group can seem all rather similar at first, so it pays to make a note of leaf detail and to take a close look at the phyllaries (the green bracts around the base of the flowerhead), which should make identification relatively straight forward.
Common Marigold Calendula officinalis
A popular garden plant that self-seeds quite freely and may be found as a weed of urban environments and disturbed ground. Flowers June to October. The flowers may be yellow or - more often - orange and are 2-7cm across. Leaves are simple and unlobed, but often have strongly wavy edges. Seedheads are very distinctive, each curved seed looking like a small caterpillar!
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Field Marigold Calendula arvensis
Introduced from mainland Europe. Occasionally reported from disturbed ground but not persisting. Recent records probably mostly come from so-called 'wildflower' mixes that are sown in urban areas. Flowers May to August. The flowers are deep yellow (rarely orange) with the flowerheads 1-2cm across. Leaves are simple and unlobed, but often have strongly wavy edges. Seedheads are distinctive spiky.
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Corn Marigold Glebionis segetum
Once abundant as a cornfield weed, this species has become very rare due to modern farming practices, but it is seeing a revival as a constituent of sown seed mixes in some arable areas, as well as in semi-natural parks, borders and suburban locations. Flowers June to September. All parts of the stems and leaves have a blue-green 'bloom' to them, which can be rubbed off with the thumb, like that on a grape or plum.
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Crown Daisy Glebionis coronarium
Introduced from the Mediterranean region and not fully hardy so usually not persisting for long. Occasionally found as a garden throw-out or where perhaps self-sowing from spilt seed. Flowers June to October. Can form quite large,spreading clumps to 60cm in height. Flowers very similar to Corn Marigold, but the leaves are very deeply divided almost to the veins and do not hve the blue-green 'bloom'. Flowers may be all yellow, or bicoloured yellow and cream.
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Yellow Chamomile Cota tinctoria
Introduced as a garden plant from Europe and occasionally found as a garden throw-out or escape. Flowers July to August. Most of the chamomiles have flowers with white rays and a yellow centre, but this one differs in its all-yellow flowerheads. Thus, it could be confused with the marigolds, but is easily identified by its densely-hairy stems and leaves. The leaves have stiffly linear side lobes which are strongly toothed at the margins.
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Treasureflower Gazania rigens
Introduced from South Africa as a garden ornamental and widely cultivated as an amenity plant (especially in coastal areas), from where it occasionally spreads. Flowers July to October. A low growing, spreading perennial with linear leaves that are dark, glossy green above and felted with dense white hairs beneath. The flowers are highly variable in colour, most often yellow or orange, with or without a darker centre, but white and shades of peach or pink - with or without darker stripes - are also grown.
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Cape Daisy Hybrids Dimorphotheca cultivars
(Osteospermum cultivars) A very variable group of horticultural varieties, probably having both D. jucunda and D. ecklonis in their parentage. Currently popular cultivars are generally not frost-hardy, so do not persist where unattended, but are sometimes seen as garden throw-outs. They are typically more upright and bushy than the Cape Daisy and have shorter leaves with strongly toothed or lobed margins.
(The taxonomy of this group bounces back and forth every few years between Osteospermum and Dimorphotheca. I'll try to stay consistent with the name used on the Plants of the World Online taxonomy, but the horticultural trade and most botany references still use Osteospermum).
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Strawflower Xerochrysum bracteatum
Introduced from Australia as a garden ornamental and also occurring in the past as an unintentional introduction from wool waste. Not recorded in East Anglia recently, but may occur where garden waste is dumped. Flowers July to September. The orange, fertile flowers that form the central disk are surrounded by 7-15 rows of bracts that harden and are very persistent. The outer (smaller) bracts are translucent, while the inner (larger) rows function as petals and may be white or any shade of yellow, through orange to red or pink. The persistent flowers make this a popular plant with flower arrangers.
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Tricolour Chrysanthemum Ismelia carinata
Introduced from Morocco as a garden ornamental and occasionally found as a survivor from previous plantings or occasionally when self-seeded. Flowers July to September. A low annual plant, growing to around 80cm in height but often much less. Flowers of cultivated forms come in a wide array of colours; most are white with coloured centres, but some may be predominantly yellow or red.
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