In the islands around Amami Oshima, just north of Okinawa, Japan, there exists an odd type of Cycas revoluta known in the west as variety aurea. This is not your typical king sago, nor is it the result of poor growing conditions, bizarre horticultural techniques, or a virus. It rather is a consequence of a genetic anomaly, as we’ll see in the following picture sequence.
Cycas revoluta v. aurea is a naturally occurring form that boasts an interesting color pattern on its otherwise normal fronds – each pinna is tipped in gold. These yellow tips are attractive to some while others think it makes the plant look diseased or ill treated. To my eye, the regular pattern of yellow against the dark green of the inner pinnae is indeed attractive, particularly at a distance. In Japan it goes by the names kogane sotetsu (gold cycad) and kinbuchi sotetsu (gold rim cycad). The following is the growth cycle of a plant over the past year here in southern Japan.
In June the plant begins its flush and by early July the new fronds have matured and hardened, but remain a bright green color. If you look closely, you can see that already the very tips of the pinnae are turning yellow.
By early August the yellowing process is in full swing and the inner segments of the pinnae are now fully mature and taking on the characteristic deep green of this species.
A couple weeks later the yellow has deepened further and the plant is at its best, with little or no browning of the tips yet.
In early September the tips begin to turn brown and the yellowing process continues down the pinna’s length. By mid October this yellowing stops and the fronds stabilize in this form.
The plant remains in this condition for the rest of the winter and spring until the new flush of fronds are produced. The peak beauty of the plant is from late August into early September before the browning process begins. In truth, it is pretty from a distance all winter long since you cannot discern the browning unless you take a closer look. Some plants seem to brown more slowly than others, so likely cultural conditions are at play as well. Next year I’ll try using fungicide to see if this slows the browning down (update, April, 2013: the past summer the plant grew its fronds a bit later and the yellowing process continued throughout the winter months and seems to have peaked right at the beginning of spring. I’ll leave the old fronds on into the summer and see what happens. Happily, there has been very little browning so far, so each year seems to yield a unique result).
The yellowing process is a result of weak tissue in the outermost part of the pinnae. This is not induced through overwatering, under watering, lack of nutrition, too much fertilizer, etc., as some have supposed. Normal plants grown right alongside this one continue on without any yellowing whatsoever. Pups taken off the main plant have produced the same pattern of yellowing, hence it must indeed be a genetic trait. To what extent this effect is passed on to its progeny, I cannot say, though a certain percentage of seedings of both varieties alba and variegata do grow true from seed.
Not a plant for everyone, but very popular in Japan, this odd form of Cycas revoluta remains a fairly rare cycad in cultivation outside its native homeland.
Here’s video showing the plant from its recently flushed state in late July 2012 thru April 2013.