Sunday, March 22, 2020

Why are Anthuriums red?

One of my favorite plants is this cultivar of
Anthurium andreanum, with spathes of
pure, bright red. If treated well, it will bloom

More correctly, the title of this post should read "why are the spathes of some species of Anthurium red?' - but that's way too wordy for a title.  The fact of the matter is that there are some 1000 species of the genus Anthurium, and only a few species have red spathes.

The most commonly cultivated species is Anthurium andreanum, available in many different cultivars and hybrids. It is native to Ecuador and neighboring Columbia. Little is known about the species reproductive biology in the wild, but the bright red spathes literally scream "birds!" Well, not quite literally, but bright red colors in plants usually are an adaptation for attracting birds, either for pollination or fruit dispersal.

It has been speculated that the red to orange spathes in wild plants help birds find the ripe fruits, which they would eat, fly off, and thereby disperse the seeds. It's a common dispersal adaptation, found even in the most archaic of angiosperms (e.g. Amborella), and it may very well be true in this species, as well as many other species of Anthurium.

In all members of the Aroid family, flowers are tiny and crowded onto the elongate spadix.  There have been many observations of pollination by tiny flies, beetles and other insects in various species of Anthurium, and it has been assumed that birds would take no notice of them. That was until recently.

A 2019 article by Bleiweiss et al. provides the best evidence so far for bird-pollination in Anthuriums with red or other brightly colored spathes. It wasn't the first evidence of the possibility, as Bleiweiss cites a paper from some 20 years earlier by Kraemer and Schmitt making similar, if not as thorough, observations.

This reminded me of seeing nectar drops on an Anthurium andreanum specimen in the Bailey Hortorium greenhouse at Cornell, some 50 years ago, and wondering the same thing.  That picture is posted below. You can see the nectar exuding from several of the tiny flowers.  A patient hummingbird could get a decent meal by collecting a series of these droplets.

Makes me think about some other pollination mysteries ... stay tuned.
Anthurium andreanum growing in a greenhouse at Cornell University around 1970. note the tiny droplets on some of the upper flowers (enlarged below).


  1. So, male and female flowers on same spadix? Would this be monoecious with distinct sexed and separate flowers? Male generally on top and female on bottom. Is there ever separate male/female spadix's on same plant??? Thanks

    1. There are several different arrangements in Aroids. Some have separate zones of male and female flowers on one spadix. In Anthurium, however, flowers are all bisexual. When the spathes first open, the stigmas are receptive, and may receive pollen from a different inflorescence. Later, the stamens, which surround each stigma, expand and release their pollen. Apparently, the drops of nectar persist through both female and male phases, providing a reward for pollinators.

  2. Wow, thank you. Didn't realize they were bisexual (hermaphroditic?). Thought they all had those separate male and female flower zones. Thanks!!