Growing Green Milkweed

This summer we harvested seed pods from 25 Green Milkweed (Asclepias viridiflora) plants in the study area. Green Milkweed is uncommon and seems to be declining in our study area. This species prefers similar habitat to Echinacea. Plants tend to be sporadically distributed across dry prairies on steep hillsides, sandy soils, and well-drained gravelly areas. Our experience has been that flowering plants often fail to produce seed. We rarely find more than a handful of plants that produce pods in a given year.

After harvesting and drying seeds, Jared cleaned seed by removing their fluffy coma. Jared then counted all the seeds and randomly selected a minimum of 30 seeds for x-raying. X-rays revealed variation. Some ovules lacked an embryo , others had whole, intact embryos. Many ovlues fell somewhere in between. They contained embryos that were undersized, shriveled, or fragmented. There was no external evidence of seed predation. The proportion of full ovules ranged from 0 to 100 percent. We are not sure whether “partials” reflect resource limitation and seed abortion, a form of late-acting self-incompatibility, or something else entirely. We are doing some research to help us interpret the biology underlying these patterns.

After cleaning, counting, and classifying, Jared prepared a subset of Green Milkweed seed for germination. CBG’s production greenhouse will germinate and grow 392 milkweed seedlings representing 15 maternal lines. We will plant these seedlings in an area south of P8. Although these plants grow slowly, our hope is that they will be an excellent resource for investigating milkweed pollination in a couple years. We also hope to harvest seed from these plants and include Green Milkweed in our seed mixes for restoration!

2021 Update: Asclepias viridiflora demography

In summer 2021, Team Echinacea searched for and mapped 71 Green Milkweed (Asclepias viridiflora) plants across 8 patches of remnant prairie in our study area in western MN. This denizen of dry prairies is tough to spot and appears to be declining across its range. Our goal is to monitor Green Milkweed individuals in the study area to better understand their demography, responses to prescribed fire, and reproduction. We located and mapped 70 Green Milkweed plants, 59 of which flowered. Of the plants that flowered, 31 produced pods. We harvested pods from 22 plants for further study in the lab and (hopefully) growing some plants from seed.

  • Start year: 2021
  • Location: Remnant patches of prairie in and around Solem Township, MN
  • Overlaps with: NA
  • Data collected: demographic data: ~Dropbox/burnRems/remAv/data2021/ascvir2021.csv
  • Samples or specimens collected: Pods/seed collected during summer 2021 currently reside in Jared’s office. These seeds need to be inventoried, cleaned, counted, and x-rayed.
  • Products: Stay tuned!

You can read more about the Asclepias viridiflora demography project, as well as links to prior flog entries about this experiment, on the background page for this experiment.

The end of summer

As summer’s vibrant greens give way to fall’s golden glow, Team Echinacea remains hard at work in western MN. A skeleton crew is diligently wrapping up the field season. Our most important task is harvesting seed from study species so that we can quantify fire effects on plant reproduction in remnant prairies. Here is a brief update on progress for our focal species:

Echinacea angustifolia harvest: 383/383 plants harvested

Andropogon gerardii harvest: 370/370 plots measured and harvested

Liatris aspera harvest: 202/231 plants harvested

Lilium philadelphicum harvest: 79/80 plants harvested

Asclepias viridiflora: all plants harvested (~30, Jared forgot to check harvest data sheet…)

In addition to wrapping up the harvest, we are beginning to make preparations for fall burns and getting materials organized to implement a seed addition experiment designed to assess fire effects on seedling emergence and survival.