Milkweed and Swallowwort

Milkweed noun - Any of numerous plants of the genus Asclepias having milky juice and pods that split open releasing seeds with downy tufts.

Swallowwort and milkweed are semantically related. In some cases you can replace term "Swallowwort" with "Milkweed", this nouns are similar.

Swallowwort noun - Tropical herb having orange-red flowers followed by pods suggesting a swallow with outspread wings; a weed throughout the tropics.

Milkweed and swallowwort are semantically related. You can use "Milkweed" instead a noun "Swallowwort".