We have several milkweed species on the trail. You can see three of them near Barmouth. All milkweeds have similar flowers and fruits. Most of them have flowers that are highly visited by pollinators. Here is a brief comparison of the three you can see here.
Asclepias incarnata, swamp milkweed
As the common name indicates, in the wild this species is found in wet areas. However it does quite well in average soils. Flowers are pink and fragrant. The flowers are highly attractive to a wide range of pollinators. Monarch butterflies will lay eggs on it but it is used much less frequently than common milkweed.
Asclepias tuberosa, butterflyweed
Popular milkweed with orange flowers, not at all aggressive in gardens. Despite the common name, of the three species described here this one is the least valuable for monarch caterpillars, according to the study referenced below.
Asclepias syrica, common milkweed
This is the species much preferred by Monarchs for laying their eggs. This species is considerably less desirable as a garden plant because it is quite spready. If you take a look near the gate to the cemetery, you can see that it has even spread into the lawn and survives mowing.
Read more about its use for monarch caterpillars and an experiment to make it even more useful.