With the help of other amateur fungi enthusiasts, I have established that the most recognisable physical difference (for amateurs) between Suillus luteus and Suillus granulatus is the presence or absence of a ring or annulus.
Freshly emerged Suillus luteus have a gelatinous coating
Suillus luteus (commonly called Slippery Jack) is mychorrhizal with various exotic conifers, meaning that it forms a symbiotic relationship with pines. Therefore, people who are fond of eating wild mushrooms can often pick up a feed (yes, they are reported to be edible) amongst, or on the outskirts, of pine plantations. However, I can not vouch for their palatability. Both Suillus luteus and Suillus granulatus were introduced to Australia from Europe with exotic trees.
Caps are convex (dome-shaped) at first, and very glutinous (jelly-like). They flatten as they mature, reaching a diameter of up to 150mm, and are viscid (sticky or slimy).
The partial veil tears away from the cap
Pores are yellow, aging to a dirty yellow. A brown annulus forms on the upper portion of the stem, sometimes falling off leaving a purplish brown band or stain. The white or cream stem (or stipe) is covered in fine brown speckles. Spore print is yellow-brown.
Speckled stem and remnants of a ring
Yellow pores age to a dirty yellow, and flesh is pale yellow
My sightings of Suillus luteus
[This will be updated with new sightings]
Hanging Rock, NSW - in and around pine plantations - Mar, Apr, May.
Mount Royal National Park - under exotic pines - Jun.
I encountered collectors in pine plantations of Hanging Rock. They sliced the fungi and spread them out to dry.