The medicinal herb, Rhodiola rosea is dioecious. Either plants will have pistils and no stamens or vice versa. That means each Rhodiola rosea plant is either male or female and the differences can be obvious.
The picture above was taken in mid-May 2022. The Rhodiola has awakened from the long winter dormancy and is rapidly growing. Spring buds on this plant had emerged and started turning green only two weeks prior to the photo.
Which one is which?
The picture shows one male and one female plant side by side. Which one is which? There are two clues in the picture. Firstly, the plant on the right has dried shoots with seed pods from last year. That’s a dead give-away. But if the seed pods had been broken off, how could you determine the gender?
Next clue – the male flowers bloom first. A week or so before the females come into flower, the male flowers are maturing and will be ripe with pollen just in time for the female flowers to open up. Often in nature the period of time for the female flower to be receptive and ready for pollination is short. Since the growing season for Rhodiola is short to begin with, timing for pollination and seed set may be critical.
The next pictures show the mature flowers of both genders. Pistils are only on the male flowers and stamens are unique to the female flowers.
Here are some other observations on plant gender in Rhodiola:
Differences in Tolerance to Cold Weather
Male plants of some strains are not as cold tolerant as females. The females are tougher? What’s that all about? In our sheltered nursery new strains are germinated and spend their first winter in raised tables about 4 feet off the ground. That makes weeding easier, but the roots of the plants are exposed to colder temperatures than if planted in the ground.
In the nursery mature plants of select strains are also grown in the raised tables for seed harvest. To our disappointment, the mature male plants for our current best strain have died every winter. Fortunately, the seedlings of this strain survive well over their first winter in the raised tables and are available for pollination purposes. In addition, male plants of this strain fare well in the field, and we bring some of these males back from the field to ensure adequate pollen.
But why would the male plants selectively die out? We know that some strains of Rhodiola rosea grow north of the Arctic Circle, an environment much colder than Alberta, Canada. We also know that wild strains of Rhodiola rosea are unique and have developed to thrive in their specific environments. Not all of them grow well in our climate. So possibly our strain with tougher cold-tolerant females has met its match for cold weather here is Alberta. And so we keep testing to find the best strains.
Differences in Rosavins
Tests by the Alberta Agriculture and Forestry indicated that the male plants had slightly higher levels of total rosavins. This result is from a small sample of Rhodiola roots. Additional testing is required to confirm this observation.
