Hylomecon japonica is a fairly rare plant that is miss-identified frequently on the internet and in seed exchanges. The AGS seedex has been sending out the wrong seeds for a number of year and discussions on their forum make it clear that getting seed from the right plant has been a global problem (ref 1).
Instead of receiving Hylomecon japonica seed, it is common to get seed from one of the other wood poppies. Since I grow Hylomecon japonica and it’s 3 imposters I decided to prepare a complete review of the plants, and provide a list of features that will allow people to clearly identify their plants.
All of the details are based on my plants which represents a limited set of clones. If your findings disagree with mine, please let me know by leaving a comment.
Hylomecon Japonica and Imposters
Hylomecon japonica is similar to Stylophorum diphyllum, Stylophorum lasiocarpum and Chelidonium majus. All four plants will grow in similar climates, flower in spring or early summer with yellow flowers and prefer to grow in part shade.
Hylomecon japonica is a wood poppy from Japan, China, Korea and Russia. It is a low growing perennial that forms underground tubers. By mid summer, the leaves die back and the plant receds underground. Synonyms include Chelidonium japonicum, Hylomecon vernalis, and Stylophorum japonicum.
Stylophorum diphyllum is also called a wood poppy or celandine poppy. It is a true perennial from North America. The common name, celandine poppy, is a result of this plant looking very much like Chelidonium majus, the greater celandine. Out of the four plants being discussed, this one is the best garden worthy plant.
Stylophorum lasiocarpum, commonly called Chinese celandine poppy, is a herbaceous perennial that is native to eastern to central China. Synonyms include Hylomecon lasiocarpum.
Chelidonium majus, the greater celandine is native to Europe. It is a biennial that has become an invasive weed in North America. In North America at least, it is rarely encouraged to grow in the garden because it is a bit weedy.
The following table compares the four species being discussed. Using the information provided it is fairly easy to identify any of the 4 species.
|seed pod orientation
|seed pod thickness
|seed pod texture
|seed pod length
|# of seed rows in pod
|3 or 4
|color of sap
|# of flowers per peduncle
|4 to 8
|# of peduncles per node
|up to 5
|texture on leaf surface
|hairs on leaf bottom
|few and short
|only on midrib
|leaflet at base of peduncle
|3, very small
|3 very small
|2 or 3
|2 or 3, 3 rd is smaller
1) The seed pod length for Hylomecon japonica from another grower was 1″ long, and it contained fertile seeds.
In this picture the seed of Stylophorum lasiocarpum was just collected. They show the shinny color as well as a fresh elaiosomes. The other two seeds were collected a month earlier and stored moist. The color of Styloforum diphyllum seed, at collection time, was a shinny dark brown and had prominent elaiosomes. The seed of Hylomecon japonica were a shinny brown and had a small elaiosome.
After storing seed for a month in a moist package, the smaller seed rotted. The larger two seeds were still firm. I suspect that the small seed was infertile – hence it’s small size. If that is the case, the percent of viable seed on my plants was very small this year.
Hylomecon japonica var. dissecta
1) Scottish Rock Garden Club Forum – discussion on Hylomecon japonica: http://www.srgc.net/forum/index.php?topic=7477.30
2) Photo Source for “Hylomecon japonica flower and leaves” photo: Alpsdake
3) Photo Source for “Hylomecon japonica var. dissecta” photo: www.planta.cn