The Milkweeds & Dogbanes
What are they?
Milkweeds are mostly small to medium height herbaceous perennials and are well known as being the larval food plant of Monarch butterflies. All members of the family have milky sap which contains toxic alkaloids and it is this that is taken up by the Monarchs and stored in their body tissues, thus rendering them poisonous too. Milkweeds generally have large, showy heads of colorful flowers which are popular with many insect species. Dogbanes are far less conspicuous, have smaller heads of small white flowers. They are perhaps most obvious in the fall when their long, bean-like seed pods can be seen. Typically for the family, the pods are borne in pairs.
Where are they found?
Milkweeds and dogbanes are plants of open, sunny sites with some species favoring wetlands, others dry fields.
Identification
Dogbanes can be told apart by their flowers, but be wary of intermediates as the species hybridize with each other. Milkweeds can be told by a combination of flower and leaf details.
Indian Dogbane Apocynum cannabinum
(Indian Hemp) Widespread but not particularly common in a wide range of open or semi-shaded habitats, both wet and dry. Flowers June to July.
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Butterfly Milkweed Asclepias tuberosa
A dazzling plant of open, usually sunny roadsides and other grassy places. Native, but also popular as a garden plant. Flowers June to August.
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Swamp Milkweed Asclepias incarnata
Found in all kinds of wet and swampy ground. Flowers July to August.
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Clasp-leaved Milkweed Asclepias amplexicaulis
A rare plant of old fields, roadsides and other grassy, open sites. Flowers June to July.
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Common Milkweed Asclepias syriaca
A fairly common plant of old fields, roadsides and other grassy, open sites. Flowers June to July.
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Black Swallow-wort Vincetoxicum nigrum
Native of southern Europe. Not a showy plant, but occasionally grown for curiosity as a garden plant and known from urban areas in Ocean City. Flowers June to August, sometimes later. A climbing or straggling plant with small, blackish-purple flowers. Could be mistaken for Japanese Honeysuckle when not in flower.
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