A great genus close to the sunflowers that, although often very tall, produce a very compact rootstock and are best displayed among low-growing plants.
Silphium terebinthinaceum

This and
S.laciniatum produce among the biggest, most luxuriant leaves of any hardy border perennial.

In this case they are huge and heart-shaped (like a
Colocasia or
Anthurium?) to 12ins across.

The flower stem is more slender and smooth than
laciniatum.
£9
Silphium simpsonii

A smaller species with simple green leaves and golden flowers
£8
Silphium laciniatum

Leaves to 2ft long and impressively lobed, like some huge tropical fern. The stiff bristly upright flower stem is a bonus.

Easy in any fertile, retentive soil, and best at the front of the border where its stature can be appreciated. Perfect for prairie-style plantings.
£9