These two plants can look quite similar at times. Is there a reliable way to tell the difference between the two? The following document lists a few things to look for: How to Tell the Difference Between a Dwarf & Full Size Umbrella Tree. I would appreciate comments regarding its accuracy. Is this true? I thought S. arboricola and S. actinophylla have dull and glossy leaves respectively. Indoor trees don't normally reach this size. However with age S. actinophylla becomes easier to identify due to wider and longer leaves (sign #4). Is this true? Pretty easy sign when the leaves are not green but no help otherwise. Not definitive when a plant is small. Indoor trees rarely produce flowers. Is this true? It would be a good test. Have a look at the plant in the thread Sad Looking UN-Identified plant | UBC Botanical Garden Forums. I identified it as S. arboricola but I'm not so certain now.
I am not aware of a third species with similar qualities that is being widely propagated by the industry for indoor culture. It would be fairly safe to assume a plant would be one or the other or one of their cultivars.
Leaf glossiness: I'm with you; S. actinophylla leaves tend to be glossier indoors, but there's a lot of variability on both species. Tree height: N/A for indoor plants. Leaf location: also pretty much N/A for indoor plants, though it's maybe true that S. arboricola holds its lower leaves longer, in general. Variegation: mostly reliable, though not 100%; my understanding is that S. actinophylla cultivars with variegated leaves do exist, though they're not commonly offered because the variegation is really unstable. Leaf size: mostly reliable, though there's some overlap when it comes to old S. arboricola or young S. actinophylla. Flowers: N/A for indoor plants. Smell: No idea. The number of leaflets per leaf is semi-reliable; a S. actinophylla with small leaves will often only have 3-5 leaflets per leaf, whereas the same sized S. arboricola will often have 7-8. In retail situations, you can partly go by pot size: if it's a 3- or 4-inch pot, it's almost certainly S. arboricola. S. actinophylla is rarely sold in anything smaller than 8-inch. Leaf venation is pretty reliable in my experience: if you can hold the leaf up to a light and easily see a light network of veins against a dark leaf, it's very likely to be S. actinophylla. S. arboricola leaves are thicker and don't transmit light nearly as well; what light does get through usually shows dark veins against a lighter leaf. Leaf margins: I think S. arboricola margins are always smooth, whereas S. actinophylla leaves are sometimes lightly toothed near the leaflet tips. Smooth margins don't necessarily confirm arboricola, but toothed margins are pretty definitely actinophylla. I'm fairly (~90%) certain that the plant in the link is S. actinophylla, not S. arboricola, mostly based on the number of leaflets per leaf, leaflet size, and marginal teeth.
