Green Dragon or Prolific Imposter?

(excerpted from an article in the FLNPS newsletter, Solidago, and the Adirondack Chapter of the North American Rock Garden Association newsletter, Green Dragon.)

Mis-identified plants are similar to a computer virus - if you get one you are likely to spread it to your friends. A chance meeting started me on an identification search that may have implications for several other gardeners in this region. Someone mentioned he’d acquired a "green dragon" (Arisaema dracontium) that turned out to be a weedy look-alike that was hard to eradicate. I’ve acquired A. dracontium seedlings from several sources over the past 8 years, but mostly from chapter sales or give-aways. I’ve had very mixed luck with them. Some sit there, while others grow enthusiastically.

Green dragons have a reputation for being hard to grow and slow to spread. Yet some folks in the Finger Lakes region literally give them away because "they grow like weeds". I’ve seen such clumps myself. Well, I started looking closer. There is an Asian genus, Pinellia, which looks just like Arisaema. Several species are in cultivation, and an internet search will generate a lot of information. I suggest starting with the Pinellia Page, which is informal and has nice photographs if you follow the links.

To make a long story shorter, I have some Pinellia mixed in with what I hope is some true A. dracontium. I think I have P. pedatisecta, but haven’t keyed it conclusively. I’m sure I got it from someone local. Given the contacts amongst gardeners here, Pinellia may well be all over the region’s gardens, which may be fine so long as it is properly identified, but not good if we are spreading it in the name of the native Arisaema.

How can you tell? It isn’t easy unless you have the inflorescences. The leaves of Pinellia look like A. dracontium (even to professionals like Bob Wesley, Cornell Plantations botanist) but the phenology is different and the Pinellia spadix (the "Jack" part in the pulpit) is fused to the spathe (the "pulpit") along much of its length. According to Bob Wesley, the spadix would be standing free, totally unfused, in true green dragons. So, you may have Pinellia if you notice that your "green dragons" are:

• Blooming in August (Yes, large A. dracontium do bloom later than small ones, but not that much later.)
• Still green in September (A. dracontium should have senesced by then.)
• Prolific self seeders (According to Bob Wesley, A. dracontium spreads more by offset bulbs, which occur pretty close to the original stem [within 2 inches or so], than by seedlings which occur further away.)

If you suspect you have Pinellia please keep a close eye on them until you can verify the identification with a bloom. Don’t give them away until you know for certain. If you have planted them in or near a natural area where A. dracontium grows naturally, please remove them. If you choose to keep Pinellia in your garden, and they can be attractive, if aggressive - be sure to clearly label any that you give away with correct ID and warnings. I’d dig them up before selling the house, too.

More information, provided by Dr. Nina Lambert, NARGS member:

"[Identification is aided by] noting that if it is emerging now [fall- RP] or still in full leaf, it is likely to be Pinellia, not Arisaema, specifically Pinellia pedatisecta. There is a different Pinellia menace in the spring, namely P. ternata. Both are thugs, hard to get rid of.

"On the other hand, several species are highly desirable, including P. tripartita 'Atropurpurea' (despite a propensity self-sow by the thousands, a propensity readily curbed by dead-heading or generosity to friends), Pinellia tripartita 'Dragon Tails", a newer smaller introduction with creamy variegation on the leaf now made available by Tony Avent at Plant Delight Nursery and P. cordata 'Yamazaki', first introduced by Roy Herold, now offered by Ellen Hornig at Seneca Hills Perennials. Despite a propensity to increase by bulblets, the latter is the fussiest about siting, refusing to linger if allowed to dry out during the summer, shallow enough to heave during the winter and taking itself off if over- exposed to direct sunlight. When happy, it makes a choice mat of plants and plantlets with such a perky flower that even a curmudgeon friend spontaneously referred to it as 'cute'. All three of these Pinellia produce flowers from mid-May through mid-October. Unlike some of the Arisaema, they hold their flowers clean and clear of their foliage. The flower on P. tripartita 'Atropurpurea' is an eye catcher during the summer quiet of the woodland garden, not so much flashy as on the regal side of elegant.

"As [I] mentioned, Pinellia do not produce seed encased in red berries on a banana-thick seed-head. Instead, their seed is still white, soft and slightly sticky when ripe, turning brown only when air dried, and comes in a green wrapper, like a partial rolled tortilla that unfolds when the seed is ready for release."

Update 2024: Another great reference for distinguishing Pinellia pedatisecta from Arisaema dracontium is at https://www.gardenmyths.com/arisaema-dracontium-pinellia-pedatisecta/