The males look like an opening clamshell. Female flowers have an inferior ovary behind the clamshell. The inferior ovary is one of the characteristics that make a begonia a begonia. The male flowers will usually open before the females. I save and collect pollen. Unless you have multiple peduncles, at different stages of development, you have not have pollen when you need it. I pick the flowers, remove the tepals from the flower, and drop it in an empty film canister. I leave it open overnight and then will seal it. I’ve stored the pollen from several days to many months. I usually keep my ‘pollen bank’ in a dry shed near my plants and close at hand. I know that it can also be stored in the refrigerator for long periods of time. When I’m ready to use the pollen, I take the pedicle that I left on the flower with my fingers and then lightly rub the male and female flowers together. You can often see a pollen cloud arise when you do this. I’ve also used a brush, or my finger, to collect pollen out of the canister to put on a flower brushing lightly so as not to injury the stigmatic surfaces of the female flower. You should wash the brush in alcohol and let dry to kill any residual pollen before using it again. Mark the flower! If it is selfed, something tied around the pedicle to let you it was you and not an insect that pollinated the flower will do the trick. If it is a cross, remember to label and mark it to because you won’t “remember” what you did.
After pollination takes place the female tepals should close. They may or may not drop off. The ovary will then start to enlarge and may change colors. When the seedpod is mature, it or the pedicle holding the flower will start to dry. This may take a few weeks to many months. At this point, I remove the flower and place it in an envelope, if there are many flowers from a selfing this holds them well. I write the name of the pod or the cross on the envelope and place in a dry place. After a few days, I harvest the seed. I do this in one of the following ways.
One way is to smash the seed pod(s) inside the envelope. Fold the lip of the envelope and let the seed roll out onto a clean sheet of paper. Then remove any extra debris, package and label. This works well with large quantities of seedpods, it removes the bulk of the seed and you can the do a more through cleaning of the remaining seed left in the envelope.
Another way is to take the seedpod out of the envelope and open the top. Holding the pod in one hand, take the other and twist off the top of pod where it connected with the plant. Or break in half. Either way, then pour the seed out onto a clean sheet of paper. Clean the debris, package, and label.
This is my method, there are others and you should keep trying until you find one that works for you. You are now ready for sharing and or growing.