Tricotyledon Echinocactus polycephalus seedling
As mentioned in the previous post I started a handful of Echinocactus polycephalus (SNL 91; Las Vegas, Nevada) from seed a few weeks ago. I didn't achieve impressive germination rates and many of the seedlings were killed off by mold while still enclosed in the humid atmosphere of the germination "tent" - and more have withered after I exposed the seedlings to the harsher environment outside of the plastic bag they germinated in. So for all practical purposes Echinocactus polycephalus (and E. horizonthalonius) live up to their reputation of being extremely difficult to grow from seed.
Echinocactus polycephalus seedling growing its first spines
That being said a few of the seedlings are doing great - exemplified by the Echinocactus polycephalus seedling pictured above, growing its first spines.
Tricotyledon Echinocactus polycephalus seedling - top view
Interestingly one of the Echinocactus polycephalus seedlings turned out to be a tricotyledon. Members of the Cactus family belong to the group of dicotyledons, i.e. their seedlings have two cotyledons or embryonic leaves. So evidently Echinocactus polycephalus is a dicot but for some reason this seedling decided to grow three seed leaves instead of the habitual two.
Polycotyledons could be considered freaks of nature or "mutant" plants but this seedling will probably grow up looking exactly like the other plants from the same batch. The last time I experienced a polycot seedling was some years ago when an Opuntia polyacantha var. hystricina seedling germinated with three seed leaves.
Tricotyledon Opuntia polyacantha var. hystricina seedling
Polycotyledon tomato, chile, aubergine, Cannabis, etc are regularly reported so this is by no means abnormal. It would be interesting to know though if this is affecting the plants in any way (as mentioned, the last time I experienced a tricot seedling the plant grew up to be indistinguishable from the "normal" plants). I'm also curious as to what is causing the extra seed leaves (the Opuntia seedling mentioned above was grown fresh from seed collected in the Grand Canyon; indicating to me that polycots are occurring naturally and are not (only) caused by "mutagens" in the environment).
George Engelmann : Box 14: Folder 22: Euphorbia: undated (added: 03/29/2017) - *By:* Engelmann, George,1809-1884. *Call Number:* Archives Collection 1 RG 4/1/5/1 *Contributing Library:* Missouri Botanical Garden
4 hours ago