Do you want to grow gunnera but your climate is too cold? Then Astilboides tabularis is a good alternative. It has some of the largest leaves you can grow in colder climates and it makes a strong statement in any garden. Most people who visit my garden are unfamiliar with the plant and find it very exotic. Its leaves are an odd round shape that reminds one of an umbrella or table top. They easily reach 60-90 cm (2-3 feet) in diameter.

Astilboides tabularis is also known as the shield-leaf Rogers plant, or shield-leaf Rodgersia, but most people just use the botanical name and call it astilboides. The genus name means astilbe-like in reference to its white flowers that are born on 120 cm (4 ft) stems.
It prefers shade to full shade and a wet location where it will stay green all summer long. It also grows well in a dryer location, but then the leaves usually get brown edges by late summer as the temperatures rise and water levels drop. It does not like to be submerged in water.

Wind can be a problem. The large leaves act like sails and easily capture wind which can damage the leaves. It is therefore best planted in a sheltered location.
The seeds are very small and hard to separate from the seed pod chaff. If you simply collect all of the material and spread it on soil, the seed will sprout.

Astilboides tabularis
(a-stil-BOY-dees tab-yoo-LAIR-iss)
Life Cycle: perennial
Height: 90cm (2 ft)
Bloom Time: early summer
Natural Range: Northern China, Manchuria, North Korea
Habitat: moist woodlands, near lakes and streams
Synonyms: Rodgersia tabularis
Cultivation of Astilboides tabularis:
Light: part shade to full shade
Soil: high organic matter
Water: average to moist
USDA Hardiness Zone: (3?) 4- 9
Propagation: seed, division
I would like to see a picture or have a description of the seeds, despite the fact that you say it is not necessary to isolate them from the chaff in order to grow them. Are they dark and round like poppy seeds? I don’t think they are the little light brown shreds that come off the old flowers, but maybe they are?
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.hst-j.org%2Farticles%2Fxml%2FYBLv%2F&psig=AOvVaw2oKO1M50-Hn8L_rF2ARnyj&ust=1724973495393000&source=images&cd=vfe&opi=89978449&ved=0CBQQjRxqFwoTCOCajZvpmIgDFQAAAAAdAAAAABAJ
It is hardy for me in Anchorage AK
Where is the seed pod chaff?