Looking like lichens: leaves disguised as tree trunks to avoid being eaten

by Piter Kehoma Boll

We are all familiar with animals of many species that developed interesting mechanisms to avoid being eaten. This includes, for example, animals that look like plant parts:

The famous giant leaf insect, Phyllium giganteum. Photo by Bernard Dupont.**

and animals that merge with the background:

An East African jackal, Canis mesomelas, in the Savanna. Can you spot it? Photo by Nevit Dilmen.***

There are also animals that look like other, unpalatable or dangerous, animals, in order to push predators away:

The edible viceroy butterfly Limenitis archippus (top) mimicks the poisonous monarch butterfly Danaus plexippus (bottom). Credits to Wikimedia user DRosenbach. Photos by D. Gordon E. Robertson and Derek Ramsey.***

But we rarely think that plants also use this sort of mechanisms to avoid being eaten. There are, however, some recorded cases of similar behaviors in plants. One case is that of the plant Corydalis benecincta, whose leaves commonly have the brownish color of the surrounding rocks:

The leaves of Corydalis benecincta look like the rocks found in its natural habitat. Photo extracted from http://www.svenlandrein.com/yunnancollections/10CS2204.html

Recently, a study on plants of the genus Amorphophallus found another interesting case of mimicry. This genus, which includes the famous titan arum, usually develops a single large leaf that in some species can attain the size of a small tree or shrub. Such a gigantic leaf seems to be a perfect meal for some herbivores but, to avoid them, many species of this genus developed a series of marks along the petiole of their leaf that look like lichens or cyanobacteria.

Cyanobacteria-like marks on the petiole of Amorphophallus gigas (A); Cyanobacteria-like plus lichen-like marks also on A. gigas (B); And lichen-like marks on A. hewittii (C) and A. dactylifer (D). Extracted from Claudel et al. (2019).

With this mimicry, the petioles, which are quite tender, end up looking like a hard and old trunk that does not look that interesting as a meal for most herbivores. The lichen marks are so well represented that they can even be associated with real lichen genera. For example, the marks seen on the figures B and C above look like lichens of the genus Cryptothecia.

Lichen of the species Cryptothecia striata, which seems to be mimicked by the marks in Amorphophallus gigas and A. hewittii. Photo by Jason Hollinger.*

How and why this marks evolved across Amorphophallus species is still not well understood. Despite the hypothesis that they help the plant mimic a tree trunk, some species with small leaves also have those marks, while some with large leaves do not have any marks or have them in simpler patterns. The titan arum Amorphophallus titanum is a good example of the latter:

Amorphophallus titanum is the largest species of Amorphophallus but displays a considerably simple lichen-like pattern. Photo by flickr user Björn S.**

For a long time, plants were regarded as less dynamic organisms than animals, but in recent years our knowledge about them is increasing and showing that they are actually very versatile creatures that developed similar creative and complex strategies.

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Claudel C, Lev-Yadun S, Hetterscheid W, & Schultz M 2019. Mimicry of lichens and cyanobacteria on tree-sized Amorphophallus petioles results in their masquerade as inedible tree trunks. Bot J Linn Soc 190: 192–214.

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*Creative Commons License This work is licensed under a Creative Commons Attribution 2.0 Generic License.

**Creative Commons License This work is licensed under a Creative Commons Attribution-Share Alike 2.0 Generic License.

***Creative Commons License This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

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Filed under Botany, Evolution

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