I would use a ParamArray to process the comma
delimited ranges and then iterate each range
individually, something like this...
Function Test(ParamArray R() As Variant)

Forgive me, but I don't see how that addresses my question.

I specifically asked about passing a reference union of the form
(A1,A3,A5).
The issue is determining its size.

.....<snip

I was wondering if a parameter of the form (A1,A3,A5) is a different type
of
object than A1:A5. So if I declared myVal as Variant instead of Range,
which I should do anyway for an unrelated reason, perhaps I could
distinguish a reference union in some way programmically (e.g. like
TypeName, but I know that does not do the trick), and some property of
that object would give me its size. As I noted previously,
myVal.Rows.Count does not suffice.

Sorry, but I totally missed the point of your question when I first read
your message. I think you may be looking to count the areas, not the rows.
Given this function declaration...

Function myIRR(myVal as Variant, Optional myGuess as Double = 0.1)

consider this...

NumberOfRanges = myVal.Areas.Count

This would properly count three even if one of the ranges was a contiguous
range reference. For example, if the union was (A1,A4:A7,A9), the area count
would still be 3 even though the total number of cells is 6. You can iterate
the areas by index value. For example...

For N = 1 To myVal.Areas.Count
Debug.Print myVal.Areas(N).Address
Next

Is this what you were looking for?

--
Rick (MVP - Excel)