Answer: Iris foetidissima is an evergreen iris. This iris loves moderate shade but also does well in considerable sunlight. It grows to three feet tall or so, with large evergreen sabres of leaves that simply never fade away in the manner of the vast majority of irises.
There is no better iris for a "permanent" feature of sword leaves, though where winters fall into the teens Fahrenheit, the leaves may be damaged & need to be thinned late in winter to remove injured leaves. It is quick to recover in the spring. In your moderate winters, Iris foetidissima may have no leaf damage at all.
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