How many colours do poinsettia petals come in? At least the two or three shown in the photo above, right? Bright red, light pink, and cream? Or have you seen other colours, like yellow, ivory, white, orange, and salmon? Maybe even rare blues, purples, or teal?
Actually, poinsettia (Euphorbia pulcherrima) has no petals at all, so the correct answer is none! Those brightly-coloured structures on your Christmas poinsettia are not petals at all, but modified leaves called bracts. Cultivated poinsettias now come with coloured bracts that can be reds, whites, creams, yellow, light orange, pinks, and bi-coloured; blues, teals, purples, and truly glittery poinsettias have all been artfully painted or decorated!
In order to colour up for Christmas each year, poinsettias need their beauty sleep! In their natural environment, the tropical dry forests from northwestern Mexico to southern Guatemala, wild poinsettias, which are naturally spindly, thin, semi-woody shrubs up to 10m tall, to are triggered to shift from vegetative to reproductive growth by shorter days and longer, cooler nights, as the seasons shift from summer to autumn. The plants must experience 4-8 weeks of nights longer than 12 hours and cooler than 22.5°C to initiate the floral development process. This also involves some of the newest leaves to produce less green-pigmented chlorophyll and more red-pigmented anthocyanins, eventually transitioning into fully coloured bracts.
The over 200 million poinsettia plants grown annually for the Christmas season are either cultivated in latitudes where the night lengths naturally lengthen beyond twelve hours or are treated to extra long 14-16 hour nights under greenhouses covered with blackout curtains to promote bract colouration and flower development.
The colourful bracts are not the only pollinator attracting feature of poinsettia. While the inflorescence and cyathia are scentless, this plant has many ways to draw its pollinators closer! Researchers haven’t yet observed what pollinates poinsettias in their native ecosystems in Mexico and Guatemala. In other countries, bees, butterflies, wasps, and ants have all been spotted visiting the bright yellow mouth-like nectaries to sip the sugar-rich nectar secreted there. The nectar itself has a special secret – view the video below to see what it is!
Poinsettia nectar actually is fluorescent under UV-light, as shown in this video! This feature might help pollinators who can see light in the UV-spectrum to easily identify which nectaries are brimming over with the most nectar.
In this year’s Christmas train show display, we have 16 poinsettia cultivars on display. These were all grown elsewhere and transported in, as we do not have the capacity to impose blackout conditions on our production houses. In the pool of individuals making up any one cultivar, each plant is an exact clone of the other! This allows us to order and display hundreds of plants, identical in colour, shape, height, and form, for a beautifully uniform display!
One of the most striking cultivars in this year’s display is the aptly named ‘Red Glitter’! Featuring ivory chips and specks on bright red bracts, this bicoloured cultivar is grown not just for its beautiful bracts, but its relative heat-tolerance under production conditions, superior branching, and strong, break-resistant stems.
Visit the Christmas Train Show in Flower Dome to see ‘Red Glitter’ and the other poinsettias amid a snowy Christmas display with real, running, miniature trains!
Want to get up close and personal with poinsettias? Our last Sensory Moments – Christmas Train Show program is this Saturday, 7 December, from 10:30am to 5pm. Come see, touch, and smell our special plants and see the UV-nectar fluorescence with your own eyes!
Written by: Janelle Jung, Senior Researcher (Research and Horticulture)
A transplanted pake (Hawai'i-born Chinese), she's finding her own Singaporean roots. Every plant has a story, and Janelle helps discover and share these with colleagues and guests, hoping to spark a mutual plant passion! Ask her what plant she named her cat after!