Asclepias Syriaca (Common Milkweed) flowering date shift i

What this paper is about

Common milkweed needs insects to move its pollen, so a shift in flowering date relative to its pollinators matters.

This paper quantifies the relationship between climate variables and flowering date, as the first step toward asking whether that coordination is coming apart.

Summarised here from the abstract below. Not the authors’ words.

Abstract

The consequences of altered flowering dates due to climate change can be severe, especially for plants that rely on coordinated flower and pollinator emergence for reproduction. The plant Asclepias syriaca (Common Milkweed) relies on pollinators for movement of its pollen and evidence suggests that it has recently been declining. Given these factors and this plant's importance as a host species for the declining Danaus plexippus (Monarch Butterfly), it is critical to determine if its flowering is being modified by climate change. As a first step to answering this question I quantified the relationship between climate and flowering date for A. syriaca using data from the USA National Phenology Network repository and the National Oceanic and Atmospheric Administration. I found that temperatures were higher than they had been historically (1895-2010) and mean flowering dates occurred earlier with higher temperatures. Additionally, there is a significant negative interactive effect of temperature and year on flowering date indicating that from 2011 through 2016 higher temperatures are correlated with increasingly earlier flowering dates. The change in flowering appears to be symmetrical in regards to the flowering time distribution, in that along with the mean, both maximum and minimum flowering dates are occurring earlier, as well. There is no evidence that earlier flowering is due to earlier initial growth or results in later fruit ripening. Consequences of this shift in flowering can only be speculated upon at this point, but due to the ecological importance of A. syriaca and its susceptibility to phenological mismatch, they should be considered when developing conservation plans for A. syriaca and the organisms for which it is a host.

Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.

Milkweeds in this paper

Common Milkweed Asclepias syriaca

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APA

Milkweed USA. (2026). Asclepias Syriaca (Common Milkweed) flowering date shift in response to climate change (listing). Retrieved DATE, from https://milkweedusa.com/research/asclepias-syriaca-common-milkweed-flowering-date-shift-in-response-2018/

MLA

"Asclepias Syriaca (Common Milkweed) flowering date shift in response to climate change (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/asclepias-syriaca-common-milkweed-flowering-date-shift-in-response-2018/. Accessed DATE.

Chicago

Milkweed USA. "Asclepias Syriaca (Common Milkweed) flowering date shift in response to climate change (listing)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/research/asclepias-syriaca-common-milkweed-flowering-date-shift-in-response-2018/.

BibTeX

@misc{milkweedusa_researchasclepiassyriacacomm,
  title  = {Asclepias Syriaca (Common Milkweed) flowering date shift in response to climate change (listing)},
  author = {{Milkweed USA}},
  year   = {2026},
  url    = {https://milkweedusa.com/research/asclepias-syriaca-common-milkweed-flowering-date-shift-in-response-2018/},
  note   = {Accessed DATE}
}