Contractile roots – a journey to the center of the earth?

The repotting of Chinese Podophyllums and Roscoea always brings to mind the contractile roots, and Jules Verne’s story ;) It is time to talk about them.

So, what’s with these contractile roots?
Many species from various families and growing in a whole range of habitats are equipped with such roots. By contracting they pull down the plant at the depth considered optimal by the species.

They particularly play a role in good plant anchorage. Also, for many bulbous/tuberous and rhizomatous species they adjust the depth of these organs in the ground where they will be protected from extreme temperatures/drought; another function is to protect the apical buds from being destroyed.

As soon as possible the Podophyllum shown below will be planted out; I felt sorry seeing the long contractile roots circled at the bottom of the container. I have to give it the freedom to go deep down in the ground.

Podophyllum delavayi (syn. Dysosma) grown in a large container – notice the contractile roots, most often they have a cord-like appearance and are unbranched. Imagine how much deeper they would have like to go if planted in the ground!

Roscoea cautleyoides – purple form

It is my opinion that these roots also have a practical implication in regards to planting.

Over the years I noticed that all the Arisaema sp. and Roscoea I planted in the ground in early summer did fine, even if some species are not considered truly hardy for the zone 5. I am sure this is because they had time to go deep down to their desired depth before the cold season started.

Planting too late means that the roots won’t have time to settle at the proper depth, with a possible negative outcome.
Many times we attribute the loss of plants to the fact that they are not hardy, or the drainage wasn’t good enough, and so on….

Conclusion: plant your Roscoea, Chinese Podophyllums and Arisaema species in the ground as soon as possible and no later than June I would say (in a cold, continental climate); if not possible, keep them in pots and wait until next year.
Also, do not grow them in pots longer than necessary, they like to go in exploration towards the center of the earth!

Another practical implication when growing these species from seeds: use taller pots, even the young seedlings like to have space for ‘deep’ exploration; it’s in their nature.

Few other Roscoea tubers pictures – the invasion of the Roscoea? :0

* All plants shown in the pictures have been grown from seeds.

You may also want to read – Hunker Down and Hold On: Contractile Roots Give Skunk Cabbage Another Special Trait.