I thought I'd throw my lot in here with a few questions and statements of my experience with growing these.
Firstly let me say sometimes I think the term " variable species" sometimes is a botanical code for " I don't have the time or resources to spend much time on this species at this time".
The problem is there are to few botanists specializing in this vast area of palms.
JD himself said in the context of Pigafetta that he only gave a casual glace at this species as there were to many other palm to look at in Asia to be concerned with this.
It wasn't until some growers in Queensland confronted him with the 2 different forms that a description for the 2 species was made.
It goes to show the pressure botanists are under.
I take my hat of to them.
Somehow I think the D. madagacariensis complex is in this category, as with other Dypsis like "slick willy" v onilahensis.
One has to ask the question what constitutes variability. Is it a matter of different forms coming from the same batch of seed. Like the 2 colours of Areca vestiaria. These can be both single and multi trunked as is Areca triandra.
On the question of variability can a palm develop a heal on one form and not on the other and still be classified as the same species. This is the big question regarding "slick Willy" and onilahensis.
With this in question I have some photos that show D. madagascariensis/ mahajanga and another similar form having a heal and D. madagascariensis/ diego form and D. madagascariensis/ lucebensis not having a heal.
So the question is can the same species be healed and non healed.
D. madagascariensis/ mahajang showing a heal
Similar form Called Dypsis sp blue showing heal and spliting
D. madagascariensis/ diego form with no heal
D. madagascariensis/ lucebensis with no heal
Has anyone grown from seed a heal forming palm from the lucebensis form and also had it other than single trunk. In my 30 years of palm growing I have grown lucebensis and it has never had a heal or sucker.
I have grown the diego, mahajanga and others and they have all been consistant within the seed batches. Because I collected the seed myself I know the source trees.
I know this is a boring old plant but its good to get a better look at it.
A question for Jeff, are the trees you have growing the large single Lucebensis form with the large espanded base, or are they the multiple stem type. As you said they can produce single and multiple stems. This is true of most inherently muti stem palms.