Field of Science

Parent Child Relationships

Relationships between parents and children are complicated. This is not only true for people and animals, but it is also true for plants. In this research paper Dr. David Haig explores the relationship between mothers and their offspring in mosses.
 Haig, D. (2012). Filial mistletoes: the functional morphology of moss sporophytes Annals of Botany, 111 (3), 337-345 DOI: 10.1093/aob/mcs295

This is a figure that I am working on for 
a paper that I am writing. It is still a work
in progress. If you have any comments or
suggestions for improvement feel free to
leave them at the end of the post.
In mosses the maternal gametophyte plant and the offspring sporophyte have a lifelong relationship. The offspring remain attached to and nutritionally dependent on the maternal plant throughout its lifespan, so nutrition is a major component of their relationship. These shared resources cause a conflict. The maternal plant needs to provide enough nutrients and water to the developing offspring for it to grow and mature, however, if the offspring takes too much the maternal plant may die. The offspring, on the other hand, is out to maximize its growth, despite any negative effects to the maternal plant. Haig goes into a more detailed discussion of the genetics behind this conflict, but what particularly interests me are his interpretations of moss structures and their functions in light of this conflict.

Stomata are cells with an opening between them. These pores enable gas to enter the leaves for photosynthesis in many plants. Additionally water escapes from the plant through these pores, drawing up water from the roots to the leaves. Haig's interpretation for mosses is that the stomata in the capsule are helping the sporophyte offspring to pull water and nutrients from the maternal gametophyte at higher rates. Thus increasing the resources that it is able to acquire. Often the photosynthesis explantation for moss stomata function is invoked, but I think that this is a really good alternative hypothesis for the stomata on moss sporophytes. As Haig so aptly said, "Sporophytes suck."

He also interprets the moss calyptra in light of this struggle between offspring and maternal plant. I am running a little late for game night, so the rest of this discussion is to be continued... 


  1. Hemiparasites do maintain a higher transpiration rate than their hosts for the purpose of capturing part of the xylem stream. However here the foot is not a haustorium and not a direct connection to the xylem stream, if there was a xylem stream. Photosynthates still have to be actively transported don't they? But it may work for water.

    1. That is a good point. I hadn't thought about the constraints for nutrient transfer that might be in place due to the placenta. I did some hunting around and read that a number of mosses do have conducting cells (hydroids) located in the foot and in some species they penetrate into the gametophyte conducting strand (Ligrone et al 1993, Advances in Botanical Research). I can't recall if there have been any studies looking at rates of nutrient transfer between gametophyte and sporophyte under different environmental conditions. Seeing some data with radio-labeled carbon/sugars in the gametophyte and monitoring the transfer might shed some light on the topic. Thanks for the thoughts!

  2. I wonder if there would be differences in stomatal density among ectohydric and endohydric mosses? BTW, your drawing is great!

  3. Thanks for the compliment on the figure. Whether there are different stomatal densities depending on the water strategy of the maternal plant is an interesting question. I am not sure if anyone has looked at that. I will let you know if I find any literature about it. Cheers!


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