The close-up of the flowers of ash Fraxinus excelsior were taken by David Haines at Inverkirkaig (NC0819) on 13th April 2017. It is on first sight unremarkable, except as a characteristically fine photograph, until you start to ask why the flowers furthest from the twig look different from the nearer ones; then things get complicated.
Ash trees are described in Edward Milner’s excellent book Trees of Britain and Ireland (2011) as ‘usually dioecious (having male and female flowers on separate trees), but are variable, with some trees bearing male, female or bisexual flowers, sometimes in different years’. This information, together with the detailed illustration in part XX of Stella Ross-Craig’s multi-volume Drawings of British Plants (1964), allows us to try and unscramble David’s example. The flowers furthest from the twig appear to be bisexual, with tiny stamens at the base of the paired carpels, or if those stamens are not functional, then the flowers are female. Those nearer the twig, on separate stems, look unambiguously male, with fat stamens still to discharge their pollen. Come what may, this tree bears flowers of both sexes. Incidentally the two types of flowers appear to mature at different times, which would discourage self-fertilisation.
At least one other mystery attaches to Assynt’s ash trees, which is whether they are native to this area. Some isolated trees are thought to have been planted, such as one at the edge of Loch Ruighean an Aitinn (NC1232), which is said to have arrived as a seedling from near Drumbeg Hotel in a load of rubble used to make up the road. Elsewhere, particularly in the vicinity of Rhicarn (NC0825), there are numerous ashes, with every appearance of belonging, including the grand-daddy of all local trees on the western side of the road.
You might care to look at the flowers of any ash trees known to you, to see if you can sort them out.