Big and Bigger
As Big Ears go, you won't find a group with more large-growing members than the group that includes Alocasia macrorrhizos. My experience with these plants started over 30 years ago when I saw pictures of the white variegated form of this species. Later, I came to regard the green form of that plant as the archetypical Alocasia macrorrhizos. As the years rolled on, I became acquainted with a number of other varieties or cultivars, and have now come to understand the wide diversity within this group.
While I have never seen my archetypal plant in bloom, I have since seen many of the other macrorrhizos types in bloom. Their inflorescences are distinctive and differ from those on the A. odora types in several respects. These blooms are more elongate, the spathes are smooth with a shinier look to them, and the aroma that emanates from them at anthesis is not a particularly pleasant odor, unlike A. odora blooms. One particular characteristic is that, at male anthesis, the upper part of the spathe falls or flops back and down, away from the spadix. You'll never see that happen on A. odora inflorescences.
Getting to know the gang
Some familiar species are found in this group, such as A. portei, with pinnately lobed leaves (picture below, left), and the "Black Mac", with dark petioles and main veins (see thumbnail picture above),. One very popular member of this group is the one known as the "Borneo Giant". This plant is not the same as the legendary Alocasia robusta but it can still attain a size that will impress your friends and neighbors. If you live in a southern climate, your plant may even develop a thick trunk like a palm tree.
As a plant hybridizer, i couldn't resist the fun of mixing these up with the Odora types. My first shot at this was when I crossed A. odora with a macrorrhizos type that had mottled to reddish petioles. What I got from that cross, I named the 'Novodora', and this was years before I found out about the Borneo Giant. My Novodora grew just about as large as a Borneo Giant, but turned out to be sterile, as most crosses between these groups turn out to be.
My next attempt was crossing A. odora with A. portei, which yielded what I named Alocasia x portora. The plants turned out to be much hardier than A. portei, but they also proved to be sterile. However, a recent cross I did between the Borneo Giant and A. portei has produced fertile offspring. This is just as I would expect from crossing two macrorrhizos types.
Alocasia macrorrhizos 'Lutea' is a stunning specimen with bright yellow petioles and main veins, and one that requires consistently warm day and night temperatures in order to attain significant size (see picture at right). In fact, this is a general rule for all of the macrorrhizos types; some are more sensitive to cool temperatures than others. As you seek these plants out, you should keep this in mind if your area is one of those where warm days and nights are not common. Consistently cool temperatures will slow the growth of these plants, frost will damage them, and a freeze will kill them. These plants need a well draining and organically rich soil medium, along with plenty of moisture. I have also found that these Big Ears benefit from being grown in large raised beds. They are heavy feeders as well so you need to keep them amply fertilized if you want to see these plants grow at their best.
See the differences
Some of the species in this group are diverse in themselves. For example, I've seen and grown several varieties of A. portei. The one most widely available on the market is from tissue culture and is markedly different from the one I used for my original Portora cross. I've even seen one exquisitely beautiful variety with very undulated leaf margins. Since most Alocasia species now available are tissue culture (TC) clones, you will do well to scout out aroid collectors and see if you can acquire different varieties that are not from TC.
All in all, you are sure to find a large Ear for your tropical corner or garden in this group.
Photo credit: LariAnn Garner, Aroidia Research