Cannot be mistaken for : any other Scabious because of its tall 2m height and large pale-yellow flowers.
Some similarities to : Small Teasel (Dipsacus pilosus) but that is shorter at 1.5m and has white flowers with long thin and narrow bracts which are yellow-green. the leaves are also very different.
Slight resemblance to :
Yellow Teasel (Dipsacus strigosus) which also has yellow florets but they are interspersed by long thin narrow bracts which are green.
Uniquely identifiable characteristics
Distinguishing Feature :
A garden plant that also sometimes escapes into the wild from where it may escape and persist in scattered places on waste ground or on rough grassy places, although your Author has never seen it growing wild.
There is a shorter Cephalarea called
Syrian Scabious which is commonly grown in gardens, Cephalaria syriaca but at only 1m that is half the height and has blue flowers. This can also escape.
Although its common name is a Scabious, all those belong to differing genera, although they all reside in the Teasel Family (Dipsacaceae)
Note that Small Scabious (Scabiosa columbaria), Field Scabious (Knautia arvensis), Devil's-bit Scabious (Succisa pratensis) and
Giant Scabious (Cephalaria gigantea) all belong in differing genera (although all four reside in the same Dipsaacaceae family).
A SIMPLE ALKALOID
Giant Scabious contains a simple alkaloid called
Gentianadine, which is also found in Gentiana turkestanorum, a non-native Gentian. Gentianidine is a pyridine moiety (on the right) fused to an Oxan-2-one moiety (left). It is a lactone.
It also contains eight cytotoxic triterpenoid saponins of the Oleanane type known as
Giganteosides, being Giganteoside A-E and Giganteoside L, M and N.
These should not be confused with a double glycoside of Quercetin called
Gigantoside A, which was found in Giant Scabious in 2006, along with Luteolin, Quercetin plus
Quercimeritrin, the latter two being single glycosides of Flavonols.