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An excerpt from Daniel Chitwood, Ph.D., assistant member at the Danforth Center as the February guest contributor for PLOS Genetics blog discussing the image from Ranjan et al. Multicellularity – especially in animals – is considered to be an important prerequisite for complex morphologies that it can enable. Land plants, too, are multicellular organisms that possess exquisite architectures comprised of leaf, stem, and root-like structures. Remarkably, from the mosses to the flowering plants, these organs arose independently multiple times during land plant evolution – an example of convergent morphology, suggesting functional significance conferred by similar structures.
But plants comprise many more lineages than just the land plants, and also include the green algae. Among the green algae are a plethora of shapes and forms . There are single celled flagellated species like Chlamydomonas, and some green algae species can form spherical colonies, like in Volvox. Other multicellular lineages of green algae, like Trentepohlia, even became terrestrial, independently of the land plants, sometimes forming symbiotic lichens.
Some green algae are giant, single celled organisms with varied and complex morphologies; Acetabularia, with an anchoring rhizoid and mushroom-like cap, possesses a single, giant macronucleus. Grafting experiments betweenAcetabularia species with different shapes provided some of the first evidence that the nucleus contains genetic information . Other siphonous algae, likeCaulerpa, are true coenocytes, with multiple, numerous nuclei. Caulerpa species have been argued to be the largest free-living single celled organisms in the world, with stolons sometimes meters in length iteratively producing fronds that can be up to 60-80 cm long. One particular species, Caulerpa taxifolia, is especially interesting. It has been dubbed the “killer alga” and has been argued to have invaded coastal ecosystems around the world. Within its cytoplasm are endosymbiotic bacteria that may help in the uptake of nutrients from the holdfast, and it can completely regenerate itself if fragmented.
| single celled organismPlant scienceDan ChitwoodCaulerpa