You have to love arisaemas. They are notable for their ability to change sex. When immature or not growing strongly, they are male. When romping away with vim and vigour, they become female and capable of setting seed. The poor weak male will still flower but is only suitable as a pollen donor. Should the female weaken itself by setting too much seed or coming under stress, it will have a little rest, becoming a male again. Is this a commentary on the human condition, I ask.
A. sikokianum is a Japanese species, remarkable because it is one of the few which holds it head above the foliage. Most varieties hide coyly beneath a canopy of leaves but sikokianum stands erect and proud, and somewhat phallic in appearance even when female. It grows from a flattish, circular corm but the problem is that, unlike most corms, bulbs and tubers (including most other arisaemas), it doesn’t multiply and set offshoots. You have to gather seed to increase it by raising them in pots or seed trays. But it is worth the effort to get a little clump or drift because the flowers last for weeks and are truly eye-catching. These are woodland plants, happiest with a light canopy of trees above, and humus rich soil which never dries out but which never gets waterlogged.
Arisaemas belong to the Araceae family which also includes arum lilies and the mouse plant (arisarum). You may have picked certain similarities in appearance, though they are not close relatives. A. sikokianum is available in New Zealand though you will have to search it out. These treasures are not standard garden department fare in this day and age. We also have quite a bit of success with A. speciosum (which is easy to grow and multiply) and A. candidissimum, if you find them available but we struggle with some of the showy varieties which need more of a winter chill.