Sunday, July 31, 2011

In Which I Attempt to Fascinate You with a Minor Plant Pigment

The Amaranthaceae, or Amaranth Family, is a somewhat obscure plant family, but you'd never know it on the farm right now.  There are amaranth crops, escaped amaranth hybrids from last year, and native amaranth weeds taking over the farm this time of summer.  It's a colorful explosion of dramatic bloomers with other meek yet ubiquitous volunteers growing between the rows of actual crops.

The hoop house, a sort of open-sided green house, is bursting with ornamental cock's combs right now.  Cock's combs are in the genus Celosia, and they come in amazing colors: eye-searing red, blazing peach with yellow, glowing whitish-green and orange.  They are such shockingly bright colors due to the fact that they are fluorescent.  Fluorescent colors absorb light energy from outside the visible spectrum (like UV light) and then emit that UV light as visible they do actually glow.  Fluorescence is most noticeable when visible lights are turned off and black lights are shined, but cock's combs are so fluorescent that you notice them in full sunlight.

Hoop house full of Celosias.

A Celosia close-up.  It's even brighter in real life.
Members of the Amaranthaceae and a few other closely-related plant families can fluoresce because they have an unusual class of plant pigments.  Most plants that have red parts use a plant pigment called anthocyanin.  Think maple leaves in the fall and apple skins.  The amaranths use a group of pigments called betalains for all their red and most of their yellow coloration.  Betalains are antioxidants, so they may have anti-cancer properties.  Betalains are also useful as dyes for food and cloth, but I doubt they are what make highlighter pens fluoresce. 

The fluorescence of cock's combs is useful for the plant - it attracts pollinators.  In the hoop house, the peach cock's combs were the hands-down favorite of bees and wasps.  Each plant was swarmed with pollinators large and small.  The peach sector of the hoop house was buzzing, audibly as well as visually, with insect activity.  Good thing I got over my giant ground hornet fear in the previous post. 

Peach Celosia, source.

Amaranths in the U.S. are herbs, though there are some tropical shrubs.  They have tiny flowers, usually clustered all together.  The flower parts are so tiny, they are best seen with a hand lens or dissecting microscope.  Other ornamental amaranths include Gomphrena and IresineEdible amaranth, genus Amaranthus, is used as a grain.  It is an important high-protein cereal native to South America.  Weedy pigweeds, in the same genus as edible amaranth, are found here in the U. S., and though their seeds and leaves are edible, it is much more of a nuisance than a valued crop. 

On the farm, half of our interactions with amaranths involve planting and harvesting the Celosias and Gomphrenas and the other half are killing the pigweeds, spiny amaranths and escapees from last year's crops.  The escaped plants from last year are seeds that have fallen and overwintered in the soil.  They are usually crosses between different types of Celosias, so they have a blend of their parents' traits.  That means they might have unpredictable colors, small flower heads and irregular growth forms.  They don't usually make good cut flowers, and they have to be treated as regular weeds. 
An escaped and hybridized Celosia from last year's crop growing among the zinnias.
And here is your reward (or punishment, depending on your sensibilities) for reading to the end of the post:  Beets are in a closely-related plant family, the Chenopodiaceae, and their red pigment is also a type of betalain.  I have never really noticed fluorescence in beets, but I haven't tried them with a black light.  If you eat a lot of beets, you may have noticed one of the disconcerting properties of betalain.  Betalain is not readily digested by humans, and it either passes straight through the digestive tract or is absorbed into the blood and eventually filtered into the urine.  Either way, the betalains end up in the toilet bowl, the same color as when they were swallowed.

1 comment:

  1. In my garden, some celosias are spiking, other blossoms are near the roots, some are a combination of both!