Lasting or existing only for a short time: evanescent, fleet, fleeting, fugacious, fugitive, momentary, passing, short-lived, temporal, temporary, transient, transitory.
The following species are considered to be Ephemerals because they grow and flower and then go dormant until the next year.
This cycle may happen very quickly, sometimes within just a few weeks or may take several months to complete. The plant will look like it is dying i.e. the leaves start to yellow and drop, even though it may be getting sufficient water. If you take a look at the root system however, it should look healthy and firm. Dicentra cucullaria roots look like clumps of little, white, fat grubs!
The following species go dormant after flowering although they are not considered to be ephemeral. These go dormant in mid-summer and the description above applies.
ALLIUM aflatuense Purple Sensation
ALLIUM x Globemaster
DICENTRA spectabilis varieties
PAEONIA tenuifolia plena
PAPAVER orientalis varieties.