Mexican Marigolds
What are they?
The English name 'marigold' really belongs to Calendula officinalis, a species that has been in cultivation in Europe since ancient times. Over time, however, it has become applied to a range of orange or yellow members of the daisy family (Asteraceae) and especially to plants in the genus Tagetes, which are often grown in cultivation as African Marigolds or French Marigolds, with a number of other Tagetes species being grown more recently, as well as hybrids and many selected varieties. Here, I have referred to this group as a whole under the name of 'Mexican Marigolds'. This is because, despite the common names of some of the species in cultivation, these plants originate from Central America and mostly from the drier parts of Mexico.
Where are they found?
These plants are commonly grown in cultivation and may set seed readily. They may turn up in a range of urban environments where they have self-seeded or where garden waste has been deposited, but plants are not frost-hardy and do not survive for long.
Identification
Plants in this group are highly variable in appearance (largely due to horticultural breeding) which can complicate identification. As a group, they typically have yellow or orange flowerheads with the number of petals (ligules) in true species being five, but double-flowered forms are popular in cultivation with petals increasing in number right up to fully pompom-shaped heads with countless petals. Typically for members of the daisy family, each flowerhead consists of many flowers and the whole is held together by a series of greenish bracts around the base known as phyllaries. In Tagetes, these phyllaries are fused together for much of their length to form a tube around the base of the flower and identification of the various species requires noting details of the measurements of the fused section of the phyllaries and of the length of the ligules (the unusual petal arrangement of members of the aster family requires the use of the word 'ligules' to define their spetals).
French Marigold Tagetes patula
Introduced from Central America as an ornamental and widely grown in parks and amenity areas as a bedding plant. Occasionally self seeds in urban environments or persists for a short time where garden waste is deposited. Flowers July to September or until the first frosts. Stems rounded, leaves up to 10cm long. Flowerheads 20-45mm across with phyllary tube 6-7mm wide and individual ligules typically 8-10mm long.
 |
 |
 |
 |
| |
|
|
|
 |
 |
||
| |
|
Signet Marigold Tagetes tenuifolia
Introduced from Central America as an ornamental and grown in parks and amenity areas as a bedding plant. There are currently no records of this species in our region, but it is increasingly grown as an ornamental and early records may have been presumed to be the very similar French Marigold. Flowers July to September or until the first frosts. Stems rounded, leaves 5-13cm long. Flowerheads up to 50mm across with phyllary tube 4-5mm wide and individual ligules typically 7-8mm long.
 |
 |
 |
 |
| |
|
|
|
 |
 |
 |
|
| |
|
|
African Marigold Tagetes erecta
Introduced from Central America as an ornamental and grown in parks and amenity areas as a bedding plant. Occasionally appears as a short-lived survivor where garden waste is dumped. Flowers July to September or until the first frosts. Stem slightly angled, hollow and swollen towards the top where it tapers into the flowerhead, leaves 5-12cm long. Flowerheads up to 70mm (or more) across with phyllary tube 4-8mm wide and ligules lemon yellow to bright orange in colour.
 |
 |
 |
|
| |
|
|
|
 |
 |
 |
 |
| |
|
|
|