Annotating the common witch-hazel
I’ve been obsessed with this species lately. It is one of the most interesting species I’ve ever studied.
All observations of the common witch-hazel (Hamamelis virginiana) in Vermont have been annotated (at least all observations that can be annotated). The results mostly agree with what’s in the literature but there are a couple of surprises. Check out the Plant Phenology chart on the taxon page (suitably restricted to Vermont). Briefly:
- Flower budding: [July–]August–October
- Flowering: September–November[–December]
- Resting: [December–]January–April
- Fruiting: May–October[–November]
Based on the number of iNat observations (a criterion that can be misleading), peak flower budding, peak flowering, and peak fruiting occur in September, October, and July, respectively. For more information:
- Annotating the common witch-hazel (googledoc)
Comments welcome.
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This may be another example of a situation for which we need new vocabulary. Since fruits must emerge from fertilized flowers, the period from December to April, during which the shrubs appear to be dormant, must actually be a period of invisible gestation. The fruits must begin to form, at some level, by the end of the flowering period, even if they don't become big enough for photographers to notice them until the following May.
Can you add the dates during which flower budding has been observed? It is worth pointing out that when buds and fruits are observed together on the same branch (August-October?), those fruits are the ones that formed from last year's flowers, not the current year's flowers. In so many other plants (e.g. Brassicaceae, Asteraceae), when one sees buds, flowers and fruits simultaneously, those fruits formed in the current year, same cycle.
@tsn thanks for the comments. You raise two important points. I'll try to address the first one in this reply. The short answer to your first question is: I believe that pollination occurs pre-winter but fertilization is postponed until the spring. See the extensive comments in this observation: https://www.inaturalist.org/observations/67878565
Thank you for the link. I always thought, simplistically, that pollination and fertilization were the same thing, happening at the same time. If those two events can be separated, I doubt that anything visible happens to mark the occasion(s). Thus, I am still hoping that there might be some way, other than simply "dormant," to describe the time of latent fertility in January - April. In the discussion to which you linked, Alex describes this stage as (very slowly) developing fruit.
Yes, I'm suggesting that pollination and fertilization are separated by months of time, but I don't have sufficient sources to back that up. It's a claim.
@ajwright can you weigh in here? Do you have detailed knowledge of this species?
See this article: https://pubmed.ncbi.nlm.nih.gov/21669713/
One of the more intriguing aspects of the reproductive biology of H. virginiana is the temporal separation of pollination and fertilization (Shoemaker, 1905; Flint, 1957). Pollen transfer and some pollen tube growth occur during the flowering period in the autumn, but fertilization does not occur until the following spring, around the time new leaves are produced. The capsular fruits develop during the growing season, reach maturity (10–14 mm in length) in late August, and remain on the plant even after the next year's flowering commences. The two seeds (5–9 mm) are ballistically ejected as the capsule dries and dehisces (Berry, 1923).
Thank you for the link and references. Fascinating! I didn't realize that such an arrangement was possible in plants.
A species well worth obsession! Keep in mind that in the animal kingdom, a process called embryonic diapause is well known to suspend embryonic development temporarily:
https://pubmed.ncbi.nlm.nih.gov/25023682/#:~:text=Embryonic%20diapause%2C%20the%20temporary%20suspension,over%20130%20species%20of%20mammals.
Why not in some plants, too?
I don't know of any other flowering plant species that delays fertilization for so long (or at all).
@cgbb2004 thanks for the reference. There's a wikipedia article on embryonic diapause as well.
@tsn I added "flower budding" to the list above as requested. I also added the relevant search URLs to the googledoc.
AFAIK, there is no way to search for observations with both "fruiting" and "flowering", say. You have to find them and mark them in some way. I added links to some interesting observations in the googledoc. This is one of my favorites: https://www.inaturalist.org/observations/186098215
Thank you for adding the flower budding dates.
Yes, that's a good observation - simultaneous buds, flowers and fruits!
The flowering phenology of Hamamelis virginiana is summarized in wikipedia. As reported in the literature, fruiting begins around the middle of May with the fruits reaching maturity by late August. However, the rest of its fruiting habit is not well known. Based on iNat observations, the seeds are dispersed by late October, but the empty seed pod remains attached to the plant, sometimes for months. (If you find a reliable secondary source that confirms these observations, please let me know.)
I took a screenshot of the Plant Phenology chart on the taxon page for Hamamelis virginiana and uploaded it to the forum: Why is “no evidence of flowering” included in the chart?
For comparison, fertilization of Hamamelis virginiana is delayed about six months after pollination whereas fertilization of Quercus rubra (red oak) is delayed about twelve months after pollination. Quercus velutina (black oak) is similar to red oak.
Fascinating!
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