The reproductive system and organs of plants are extremely varied and complex, and worthy of an entire website to themselves – a comprehensive view is beyond the scope of this website. But what I want to do is provide a bit of information to help you identify which buds might be reproductive vs vegetative.
There are different buds for vegetative (shoots & leaves) and reproductive (flowers, strobili) organs – within each bud a different set of components develop depending on what kind of bud it is. For angiosperms, it’s hypothesised that flower buds are based on the same structures as vegetative buds – that is, a bud starts as vegetative and then differentiates into a flower bud.ref For gymnosperms, reproductive buds contain male or female strobili.ref These are the male pollen cones or the female seed cones.
There are two ways to work out which bud is which – by their appearance or by their position on the tree. The appearance route is best aided by dissecting some actual buds from the tree you are interested in, so you have real data from the real tree. Otherwise, read on for more information about how vegetative and flower buds differ in appearance.
Vegetative buds are “encased by strong, coarse, mature scale leaves. Thinner, more membranous scale leaves make up the next layer. The scale leaves form a protective enclosure surrounding the developing foliage leaves.”ref In many of the articles online, leaf buds are said to be thinner than flower buds (at least for angiosperms). Below are the vegetative buds of Acer pseudoplatanus and Fraxinus excelsiorref:
A flower bud develops sepals, petals, stamen, pistil, ovaries & anthers, instead of leaves and more buds. Below is a scanning electron micrograph of a Bing cherry flower bud forming where M is the meristem, B is the bract and F is the very start of the flower forming – the progression over time is from left to right. On the right is the pistil with ovary (O) style (SY) and stigma (SM). The scale of the image is provided by the white bar on the bottom right hand side, which is 100 micrometres (or microns) – about 1/100th of a centimetre. Obviously it’s impossible to detect a flower bud at this stage by eye, it’s way too small!
The buds of these Bing cherries started forming and were detectable under a microscope from mid-May (the location was Washington state USA) – the year before they would flower and fruit. At a lower magnification below is a progression in flower bud development of a Camellia – the key difference is that at A2 when the flower starts to differentiate, the tip of the bud becomes more rounded and flattens.
Some of the trees we use in bonsai are dioecious which means they are only male or female and not bothref. This means they will produce only one type of flower or strobili bud. To check whether your gymnosperm is dioecious or monoecious you can check the gymnosperm database. Unfortunately I don’t have a reference link for angiosperms.
In gymnosperms there are no flowers, instead the reproductive organs are male or female strobili (pollen or seed cones respectively). A brilliant reference for some of these is available online here. An extract from the publication is provided below with some examples of vegetative and male & female strobili buds.
As noted another way to determine the type of bud is by its position. To do this you need to work out what the architecture of your tree is and where buds of different types typically form. Trees conform to one of 24 architectures as described in Tree Architectural Models and these give an indication to the location of reproductive buds. Trees can have one model for their juvenile phase (before they flower or adopt mature foliage) and then one for their reproductive phase.
In the case of apple, it has been found to conform to Rauh’s model when juvenile and Scarrone’s when reproductive.ref Even with this, “great differences exist between cultivars whether they belong to “spur” vs. “spreading” or “terminal bearing” growth habit”ref
In cherry, “The long branches bear short shoots, also called spurs, in lateral positions on the distal half or two thirds of the branch with more vigorous spurs toward the distal part [the most distant part]. Flowering occurs in axillary positions on the five to six basal-most nodes of all shoots whether long or short. Floral buds are thus located exclusively on the preformed nodes of the previous year shoots.”ref
In some species, particularly pines, the long shoot buds have many different components on them in a specific order. Here is a Pinus contorta bud – you can see the male (pollen) cones appear first, and are positioned at the bottom of the final shoot, and the female (seed) cones appear last just below the top of the shoot.
A similar layout is seen in Pinus thunbergii:
As you can tell from the above, there is quite a bit of complexity in understanding the architectural model of a tree, and where different buds form, as there are many variables involved. Observation is probably going to be the better method.