Zhu's Plant Journal 
Compiled reference
Background
Frailea is a genus in the cactus family. This page stays at the genus level (Frailea spp.): I no longer know where my plant came from. It is most likely the common Frailea castanea, known in Taiwan and Japan as 士童 (shidō), but I can't be sure.
The genus was published in 1922, and POWO accepts 20 species. They are native to South America, from western Colombia and Bolivia to southern Brazil and northeastern Argentina, including Paraguay and Uruguay. The Taiwan Catalogue of Life calls the genus 士童屬; the iPlant database of the Chinese Academy of Sciences' Institute of Botany calls it 天惠球屬.
A few of the species
Several names often heard in the hobby actually belong to different species in the genus. The Chinese names listed in iPlant include:
- 士童: Frailea castanea
- 虎之子: Frailea pumila
- 天惠球: Frailea cataphracta
- 龍之子: Frailea pygmaea
- 貂之子: Frailea phaeodisca
- 紫雲殿: Frailea gracillima
- 小獅子丸: Frailea schilinzkyana
The plant usually called 士童 is Frailea castanea, native from Rio Grande do Sul in southern Brazil and Uruguay to northeastern Argentina. The formerly common name Frailea asterioides is now treated by POWO as a synonym of F. castanea.
Flowers that often stay shut
The Huntington Botanical Gardens' International Succulent Introductions (ISI) notes that Frailea are dwarf cacti whose flowers before fruiting are often cleistogamous: they pollinate themselves without ever opening. So you often see the papery, easily crumbled fruits developing without ever having seen an open flower.
CITES
Frailea is listed in CITES Appendix II under the family listing for cacti (except species in Appendix I; no Frailea species is in Appendix I).
Sources
- Royal Botanic Gardens, Kew — Plants of the World Online (POWO)： Frailea Britton & Rose
- 臺灣物種名錄 TaiCOL： Frailea 士童屬
- 中國科學院植物研究所 — iPlant 植物智： 天惠球属 Frailea
- Royal Botanic Gardens, Kew — Plants of the World Online (POWO)： Frailea castanea Backeb.
- The Huntington Botanical Gardens — International Succulent Introductions（刊於 Cactus and Succulent Journal 76(2), 2004）： Frailea gracillima subsp. horstii F. Ritter | ISI 2004
- UNEP-WCMC／CITES 秘書處 — Species+： Frailea castanea — Legal
My own observations
Cultivation
Tiny, with spines that don't hurt
Frailea is a small cactus I'm quite fond of. Why do I like it? Mainly because it's small and cute, and I seem to have a soft spot for cacti like this, with almost no protruding spines that can hurt you.
This group actually includes many kinds, and many different names are used in the trade, such as 艷肌士童, 蜈蚣丸, 虎之子 and 紫雲丸. The origin of my plant can no longer be traced, but it's most likely the ordinary 士童. I bought it from an ordinary garden shop back when I was first starting to collect small, cute plants.
Calling it small is no exaggeration
Calling it small is no exaggeration. You can see a mature plant (one that already fruits and sets seed): next to my finger it is still very small, yet it may already produce ripe seed.
I also photographed a plant that already fruits alongside a small seedling still being raised, for comparison. Both are in 2-inch white square pots. You can see the mature plant and the small one still differ somewhat in size, but overall both are very small.
A very short flowering period
Another rather distinctive thing about Frailea is that it's a species with a very short flowering period. In other words, when it flowers, it's sometimes over before we notice, or the flower is pollinated before it even opens, so I often see ripe fruits, full of little seeds, before I've ever seen a flower. That's why people mainly collect it for the look of the plant itself.
