In common parlance, this plant is in the general group known as "Toothbrush Grevilleas", because of the shape of the flower trusses.
Fresh flower head
That shot shows a fresh group of flowers opening - they open from the lowest end (closest to the main plant) first. The flowers at the left are just opening. Those at the right are freshly opened, with pollen obvious on the tips of the stigmas. These are the "pollen presenters" which I discussed a few weeks ago, when showing you the parts of a Waratah flower.
mature flower head
pollinated flowers starting to develop swollen ovaries,
which become "seed capsules" eventually.
Note the distinctive hairiness of the ovaries, and the stripes developing.
You can see the green floral tube (perianth), with the swollen knob on the end, where the anthers are located. The long thin structure is the "style" (longer than in a Waratah) which is still tucked into the end of the Perianth. Eventually it will open out nearly straight, protruding from the flower, to help in pollination by birds and insects.
Pollen presenter (with fresh pollen dusting on it)This shows the anthers which are housed within the top of the "perianth", but once the pollen presenter straightens out, you can see that it is actually located at the base of the total flower. There are four of these organs insuide the perianth tip, and they were touching the "pollen presenter, in the curled up position (two images above).
Two sets of paired flowers, the top one mature, and the lower one, having been pollinated, is starting to develop seeds, inside the hairy tufted ovaries. You can see where the ovary is located (deep withing the flower), in this comparison shot. What is less obvious is that the pollen grains (from another flower) must grow (literally) down the full length of a tube within the style (no longer called a pollen presenter, once it starts to function as the female organ). We tend not to think of pollen as a living organism. But when you see the journey the "germ" must make, (the pollen does not fall down an empty tube), you realise it must literally grow down the full length of the style, to reach the ovaries, within that bulbous bit at the base of the style. Quite a remarkable journey, really.
Two more comments to make. I mentioned when discussing Waratah flowers, that the botanists class them with the Grevilleas, because of the "paired flowers". This is what I mean. Within the composite flower head (truss of flowers), the flowers are arranged in pairs.
Finally, this is another species - Grevillea arenaria, and I have included it, for it shows all aspects of the discussion I have just presented, within a single image. Somehow, its parts are more conveniently arranged. The perianth segments do not seem to twist around as much as Waratahs or Grevillea rivularis do - so you can clearly see the pollen presenter, (style and stigma, with its dusting of fresh pollen) and the anthers neatly showing underneath the flower. That species has a large swollen base of the flower, which is where the ovary is located.