Observations on phenology and pollination of Triphora trianthophora (three-bird orchid) made during the summer of 2019

This post is a modified article that was originally published in the Webster Groves Nature Study Society’s journal, Nature Notes (January, 2020, Vol. 92, No. 1).

Finding the orchid, Triphora trianthophora (three-bird orchid, nodding pogonia), during open bloom can be somewhat of a chore, particularly among us weekend warriors. Casey Galvin and I were both intrigued about the possibility of getting photographs of this diminutive and gorgeous orchid since learning of their discovery at Babler State Park by the WGNSS Botany Group led by Nels Holmberg, John Oliver and others in 2018. The following descriptions and photographs are anecdotal and were not collected using rigorous scientific methodology.

Phenology

There are several reasons it is challenging to find this extremely ephemeral plant in bloom. First, being partially saprophytic, the plants exhibit periodic dormancy and may not send up above-ground shoots every year, persisting instead as subterranean tubers for extended periods (Homoya, 1992). Even when they do produce stems and leaves, there is no guarantee the plants will flower in a given year. Additionally, when they do flower, any one bloom is open for only a few hours during a single day.

Exhibiting a phenomenon known as thermoperiodicity, a group or population of these plants are synchronized to open mature buds on the same day. This first wave of synchronous blooming is reportedly induced by a drop in minimum daily temperature of at least three degrees over two or more consecutive days. Following another 48-hour period, all mature buds within the population will then open on the same day (Luer 1975). Being skeptically minded, this was something I wanted to observe for myself.

Beginning in late July, Casey and I began monitoring the easier to get to population at Babler State Park. The first wave of synchronous flowering occurred on August 3rd. We unfortunately missed this but know the exact date because of visits on days immediately before and after this date. Looking into historical temperatures collected from the closest publicly-available weather station (Babler Park Estates – KMOBALLW37) revealed the initial blooming date fit the required temperature pattern perfectly (see attached figure). I continued monitoring and collecting flowering data and observed two more large flushes of synchronized blooms along with three days interspersed where only 3–10 stems/plants opened flowers. For subsequent synchronized days, I did not observe a coinciding drop in temperature as described above. I assume that the trigger for the initial bloom works to synchronize the population and subsequent larger bloom days are consequently synchronized due to all plants ‘running ahead’ at the same rate. However, there could potentially be some other unknown environmental triggers that are playing a hand here.

The first synchronous bloom occurred on August 3rd, approximately 48 hours following a four-day drop of approximately seven degrees in minimum daily temperature. Data collected from https://www.wunderground.com/ accessed on 12/06/2019.
No longer “nodding”. Triphora trianthophora flowers open towards the sky en masse on just the right day. Photo by Bill Duncan.
Arrive a day too late and this will be what you find. Photo by Casey Galvin.
Much like the flowers, these developing pendulous seed capsules will become erect at maturity. Photo by Bill Duncan.

Pollination

Halictid bees have been reported to be the primary pollinator for this species (Luer 1975). I had this in mind as I observed and began taking photographs while visiting on a large bloom day but doubted I would be fortunate enough to observe or photograph a potential pollinator visit. However, patience allowed me to do just that. I first observed visits by small flies and Bombus impatiens. Although Williams (1994) reported that Bombus have acted as pollinators of this species, I did not observe any of these visitors with attached pollinia during the 10-15 flowers I watched them visit. Eventually, I observed three different Halictid bees as they visited multiple flowers and observed these were heavily attached with pollinia. As described by Williams (1994), seed capsule production (successful pollination) is a relatively rare event in this species. Nevertheless, this was a treat to observe and photograph.

Nectar thieving flies and developing buds can be seen along with an open flower. Photo by Casey Galvin.
Like a hand to a glove… This halictid bee (Augochlora pura) does not yet realize the burden it will be asked to take in exchange for sweet nectar. Photo by Bill Duncan.
Removing itself along with attached pollinium requires some gymnastic effort. Photo by Bill Duncan.
Removing itself along with attached pollinium requires some gymnastic effort. Photo by Bill Duncan.
If you had to make this bee anymore attractive? Augochlora pura with attached colorful Triphora trianthophora pollinium. Photo by Bill Duncan.
Bees in the genus Bombus have been described as active pollinators of Triphora trianthophora. I watched several B. impatiens each visit multiple flowers and observed no attached pollinia. Photo by Bill Duncan.

REFERENCES

Homoya, M.A. Orchids of Indiana. Indiana University Press, Indianapolis, Indiana, USA.

Luer, C.A. 1975. The Native Orchids of the United States and Canada. New York Botanical Garden, Bronx, New York, USA.

Williams, S.A. 1994. Observations on reproduction in Triphora trianthophora. Rhodora 96:30-43.

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