Thursday, April 17, 2014

Arisaema serratum: Toxic, sex-changing perennials with pitfall-trap flowers and blood-red berries.

Arisaema serratum, the Japanese arisaema, is one of the most conspicuous flowers along the trail from late March through September.  It may be the perfect flower for the Gothic gardener. Visitors inevitably point to the flowering stalks or the clump of bright red berries and ask,

"What's this flower?"

"That plant is a member of the same family as taro."

"Can you eat it? Those berries looks pretty big."

"Well. . . something, probably deer, do sometimes munch on the flowers, but if you eat it, oxalic acid molecules the shape of little needles will probably tear up your throat so badly it hurts to breathe."

"Oh. . . What's it called?"

"In English, we just call it the Japanese arisaema, but look at the coloration of the stalk. Does that remind you of snake skin? The Japanese call it mamushi-gusa, the pit-viper weed. Still want to try eating it?"

While A. serratum (synonymous with A. japonicum, but that's another can of worms!) can be found throughout Japan and is one of the most conspicuous flowers around here, there are some 30 species of arisaemas in Japan, from Okinawa to Hokkaido, and over 150 species of arisaema worldwide, but you do have to get away from the cities to find them. People in the Northern hemisphere may be family with jack-in-the-pulpit.

The Toxin: Raphide

Alocasia odora,
Elephant's ear looks
similar to taro.
This genus is in the Araceae family. The Japanese know this family best for taro, or satoimo in Japanese. This is a delicious tuber, but it is not eaten raw because of the presence of calcium oxalate crystals. If you've ever had a kidney stone, then you can probably blame the  formation of calcium oxalate within your body. (Note: I don't believe this is related to ingestion of calcium oxalate.)  Needle-shaped molecules of calcium oxalate, called raphide, are produced by many plants to deter foragers. Side effects of ingestioArisaema thunbergii Blume subsp.n can range from tingling in the tongue and mouth, to inflammation of the throat so severe  that the victim has trouble breathing. In the past 50 years, there have been no records of anyone dying from eating A. serratum in Japan, but there have been several hospitalizations. There is another member of this family, Alocasia odora, called Elephant's Ear in English, that visitors often confuse with taro, with similarly unpleasant consequences and a trip to the hospital. The Japanese name for Elephant's Ear is kuwazu-imo, meaning inedible potato. Other plants containing raphide include philodendrons and schefflera, that, together with Elephant's Ear, are often used as ornamental plants in the West. If you want to try the tingling, without hospital bill, then look for the fruit of the monstera plant, also a member of this family. (Oh, but Do Not attempt to eat the rind like the fool I was!)

The garden variety of Monstera is both beautiful
 and tasty if eaten properly.
Pitfall-trap Flowers

Of course, the reason these plants stand out so much are the shape of the pitfall-trap flowers. Carnivorous plants are famous for pitfall traps, but arisaemas simply use them as a pollination strategy. In the case of arisaemas, these organs are composed of a central stalk, called a spadix, the lower half of which is covered in tiny flowers, and a surrounding vase-like leaf, called a spathe. Insects crawl down the spathe to the flowers and have a hard time getting back out. Male plants have an opening at the bottom of the spathe, so that insects will cover themselves with pollen as they crawl down the length of the flower to escape. Female plants are not so generous.

Male flowers:
Left: Male flowers on the spadix. Right: Opening for insects to escape

Female flowers:
Left: Female flowers. Center: No opening for insects. Right: Insects trapped inside.

A. thunbergii subsp. urashima
with a beautiful array of
 leaves and an extended spadix.
One of the beautiful species of arisaema in Yakushima is called A. thunbergii subsp. urashima. The spadix has a long extension used to lure insects inside. This whip-like extension has been likened to a fishing rod, perhaps the fishing rod of Urashima in the legend of Urashima and the sea turtle kingdom. (I imagine this works the same way fly tape does:  Just try hanging a piece of string from the ceiling and open the window. Flies apparently like to land on long, skinny things.) Because of the shape of the flowering organs, Arisaemas are sometimes referred to as cobra lilies. However, true cobra-lilies are an unrelated species that captures insects for the purpose of eating, while, in the case of Arisaemas, insects become casualties of pollination and their dead bodies simply accumulate inside female flowers.

Sex-Changing Habits

Fruiting A. serratum
Okay, so I still haven't touched on what many botanists consider the most interesting trait of arisaemas: Labile sex-changing, the ability to change sexes based on growing conditions. Arisaemas are perennials that die back every year, although the underground tumor, called a corm, can continue to produce flowers for 20 years or more.  Apparently, a small corm tends to produce strictly male flowers, but when the corm grows large enough, they produce only female flowers. The reverse, although rare, is also possible. So imagine a large female specimen producing a bunch of berries that will likely fall to the ground uneaten and later spring up as males around the mother plant.

Find Them before They Find You!

An unusual specimen of A. serratum with
two stalks. A week later one flower has
been lopped off and has bite marks. Were
the deer confused by the twin stalks?
A. serratum is especially common along roadsides and mountain trails up to elevations around 900 m. The stalks start popping up in February and even after the flowes wilt, the bright, blood-red berries will remain, uneaten until after summer ends. (A. serratum is so abundant, that it got all the attention when I was training, and I ignorantly assumed it was the only Arisaema on the island! Well let me make up for that oversight now!) Look for A. urashima in the spring, from coastal plains and along the trails up to around 800 m. A. sazensou and the rare A. longipedunculatum can also sometimes be found along trails in late spring to early summer. Elephant's ear grows abundantly at low altitudes, and monstera is often found in gardens.

A. longipedunculatum


Information about sex-changing of arisaemas is discussed in depth in
  Kinoshita, E. 1987. Sex Change and Population Dynamics in Arisaema (Araceae). I. Arisaema serratum (Thunb.) Schott. Plant Species Biology 2:15-28.

and a review is given by
  Srivastava, P. and Banerji, B.K. 2012. Gender biasing in Arisaema – a unique and rare phenomenon. Current Science, 102:189-193.

A casual overview of A. serratum in Japanese with a photo of  dead insects inside a fruiting flower can be seen at
A. sazensou .

Examples of toxic plants containing raphides from .

Species identification:
  初島住彦監修, 屋久島の植物(新版). 2001:南方新社
  片野田逸朗, 九州野山の花. 2004:南方新社

It makes my head spin, but if you really want to debate names, i.e. A. serratum versus A. japonicum, then you can look up
  邑田 仁、大橋 広好. 2009. 牧野富太郎とマムシグサの分類(日本植物分類学会第7回東京大会公開シンポジウム講演記録 「牧野富太郎博士の植物研究とその継承」)  [Taxonomic history of Arisaema serratum and A. japonicum] 分類9(1):37-45.

Toxicity information and counts of poisoning incidents (I understand why little kids might eat them, but apparently some adults mistake the blood-red berries for corn? ?) are listed in  
   Ministry of Health, Labour and Welfare: 自然毒のリスクプロファイル:高等植物:テンナンショウ類 (visited on April 17, 2014).

*edited on 1/15/2015 to correct the synonym Arisaema urashima to A. thumbergii subsp. urashima.
A. serratum

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