Poinsettias Wild Origins

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Poinsettias are famous the world over for the splash of color they provide indoor spaces during the colder months of the year. The name "poinsettia" is seemingly synonymous with the holiday season. They are so common that it is all too easy to write them off as another disposable houseplant whose only purpose is to dazzle us with a few short weeks of reds and whites. With all of the focus on those colorful bracts, it is easy to lose sight of the fact that these plants have wild origins. What exactly is a poinsettia and where do they come from?

Poinsettia is the common name given to a species of shrub known scientifically as Euphorbia pulcherrima. No one quite knows the exact origin of our cultivated house guests but the species itself is native to the mountains of the Pacific slope of Mexico. It is a scraggly shrub that lives in seasonally dry tropical forests. Mature specimens can grow to be so large and lanky that they almost resemble vines. 

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These shrubs flower throughout winter and into spring. What we think of as large, showy, red and white flower petals are not petals at all. They are actually leafy bracts. Like a vast majority of Euphorbia species, E. pulcherrima produces tiny yellow flowers. They aren't much to look at with the naked eye but take a hand lens to them and you will reveal rather intriguing little structures. The bracts themselves serve similar functions as petals in that their stunning colors are there to attract potential pollinators. 

The bracts also caught the attention of horticulturists as well. Because of their beauty, E. pulcherrima is one of the most widely cultivated plants in human history. As many a poinsettia owner has come to realize, the bracts do not stay colored up all year. In fact, the whole function of these bracts is to save energy on flower production by coloring up leaves that are already in place. The key to the color change lies in the relative amount of daylight. 

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As days grow shorter, the plants begin to mature their flowers. At the same time, changes within the leafy bracts cause them to start producing pigments. When the days become shorter than the nights, the plants go into full reproductive mode. Both red- and white-colored bracts have been found in the wild. As soon as the days start to grow longer than the nights, the plants switch out of reproductive mode and the dazzling color fades. In captivity, this change is mimicked by plunging plants into complete darkness for a minimum of 12 hours per day.

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Another aspect worth considering about this species is its sap. Whereas most plants hailing from Euphorbiacea or spurge family contain toxic sap, the sap of E. pulcherrima is very mild in its toxicity and an absurd amount of plant material would have to be consumed to suffer any serious side effects. Certainly it serves an anti-herbivore purpose in the wild, however, as long as you're not a tiny insect or a gluttonous deer, you have nothing to worry about from this species at least. So there you have it, some food for thought if you feel the urge to purge some spurge in a post-holiday cleanse.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Spurge of the Sidewalk

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Meet the prostrate spurge aka Euphorbia supina aka Euphorbia maculata aka Chamaesyce maculata. Whew, that is a lot of names for such a small plant. Taxonomic struggles aside, many of you have probably seen this small forb growing all over. From fields to parking lots, and even city sidewalks, this small member of the spurge family is an early colonizer of waste places where not much else can grow. I have seen this plant my whole life but never took any notice of it's flowers. I can't say I blame myself considering their diminutive size. Like many members of the spurge family, the latex-like sap can cause a skin rash in some people, so be aware of this when weeding your garden. It is native to the lower 48 but has been introduced far and wide thanks to human activity and it's resilience in poor habitats. In at least one study, leachates from prostrate spurge were shown to inhibit nodule formation on the roots of legumes. In essence, this species may be inhibiting other early succession plant species in order to maintain open habitat for itself for as long as possible. I must say, after finally taking a closer look at this species, I have developed a new found respect for it. 

Photo Source: Wikimedia Commons

Further Reading:

http://plants.usda.gov/core/profile?symbol=chma15

http://www.jstor.org/discover/10.2307/2441417?uid=4&sid=21102522714117

The Holoparasitic Mistletoes

Flowers of   Tristerix aphyllu s

Flowers of Tristerix aphyllus

The order collectively referred to as mistletoes is incredibly diverse. They range in size from rather large trees down to little more than a couple leaves, barely recognizable on their hosts. Even more unique are the mistletoes that have foregone much of what we would readily recognize as an actual plant. These parasitic plants have adopted an endophytic lifecycle, living their entire lives within the vascular tissues of their host plants, only visible to observers when in flower. 

Tristerix aphyllus is one such species. Its hosts are cacti in the genus Echinopsis (formerly Trichocereus) native to Columbia and Chile. Being an endophyte, the majority of this mistletoe lives as a mycelial-like network of filaments that wrap around the vascular tissues of the host cactus. The only part of the mistletoe that ever emerges are the flowers. They come in both red and yellow forms. What may appear to be lovely cactus covered in red flowers are actually the flowers of Tristerix. Strangely enough, the occasional small leaf is produced on the flowering branches. Though there is chlorophyll in the leaf, researchers believe that they perform little if any photosynthesis.

Fruiting   Tristerix aphyllu s

Fruiting Tristerix aphyllus

This is not a parasitic relationship that is unique to cacti either. Africa has its own endoparasitic mistletoe as well. However, as we have discussed before, Africa does not have any native cacti (http://on.fb.me/1zPbac7). Instead, through convergent evolution, plants in the genus Euphorbia have followed similar adaptive trajectories. As such, at least one species of African mistletoe has followed suit.

Flowers of   Viscum minimum

Flowers of Viscum minimum

A species known scientifically as Viscum minimum finds the cactus-like Euphorbia horrida and E. polygona to its liking. Like Tristerix, Viscum minimum is endoparasitic, living entirely within the tissues of its Euphorbia host until it decides to flower. It too produces brightly colored berries that aid in its dispersal to a new host. 

The main seed dispersers are birds. After consumption, a bird either regurgitates the embryo or passes it out the other end. If that bird happens to be sitting on a host cactus or Euphorbia, the embryo will grow into a seedling that quickly taps into its new host and begins its internal parasitic life. It will not be seen again until it flowers.

Viscum minimum  beginning to set seed.

Viscum minimum beginning to set seed.

Photo Credit: [1] [2] [3] [4]


Further Reading: [1] [2] [3] [4]