Backyard Seed Dispersal: The Plot Thickens

After posting my last post I decided to do a little detective work. There are enough ripe Coprosma robusta fruits around so I picked several and took them apart to see what their seeds look like. Did they look the same as those I found the other day?

Unfortunately, the C. robusta seeds are not only much larger than my bird dispersed seeds, but a different shape. So I can confidently say the bird dispersed seeds I found a few days ago are not C. robusta, like I thought they might have been.  

Then, while picking up Saturday morning's walnuts from the back lawn, I came across some more bird dispersed seeds...

These ones look very much like C. robusta...

But what are these ones???

I tried cleaning off some the pulp off these new ones, and I did eventually succeed, but that pulp was horrible sticky stuff about the consistency of egg whites. It clogged up my tweezers something awful. As I was cleaning them, my mind drifted back to a university lecture I'd had a few years ago. Mistletoes are hemi-parasitic (i.e. they tap into their host tree to obtain water and nutrients, but they still photosynthesise to produce their own sugars). This means their seeds need to land on tree branches to be able to germinate and grow, instead of on the ground like most other seeds. What adaptations do they have to encourage their deposition on tree branches? They have sticky seeds. When a bird excretes a mistletoe seed (whether by regurgitation or defecation) it sticks to the bird instead of dropping to ground. To get rid of the seed, the bird must wipe it off on a branch. Although the sticky seeds I found were on the ground, I wondered if they could be mistletoe...

There is one mistletoe plant here at the farm (a green mistletoe - Ileostylus micranthus), which must have itself been brought in by the birds. So I went out to look at the mistletoe. It was covered in ripe fruit.  I collected several and pulled them apart, and this is what I found...

Seeds and fruit of Ileostylus micranthus.  Two seeds
covered in sticky pulp on the left and three whole fruits on the right.

This is very exciting – the host tree for our mistletoe is dying, and the branch the mistletoe is growing on already looks quite dead. As the mistletoe looks quite healthy one assumes the branch can't be totally dead, but its days are probably numbered. Hopefully the birds will successfully disperse one or two of its seeds to other trees, where they can germinate and grow new mistletoe plants.  

  

So we have bird dispersed C. robusta and mistletoe seeds but what were those original bird dispersed seeds I found? The mystery deepens!