Without knowing the species/cultivar that you are enquiring about this is slightly problematic, however the link provided shows images of the seeds of three species:
S.alba, S.japonica and S.tomentosa. You need to scroll down to "Images" and click on to the species required.

[For cultivation advice including seed sowing, highlight and paste into your search box:
guides 69353 site: davesgarden.com -then choose the davesgarden site.
(S. fritschiana is shown for the purpose of illustration only, you can choose the species/cultivar of interest to you)].

Here is a link that might be useful: Spiraea seed images

Thank you! Thank you ! Thank you! :)~Angie

Ok,I looked at the link you provided and I know the types I have are Japonica,no seed! Thats why I havent found any!...lol...Thank you now I can forget about it!~Angie

That info'on the Davesgarden site with regard to seed from S.japonica ("plant does not set seed, flowers are sterile, or plants will not come true from seed"),
was a "Boolean OR statement" meant as a catch-all, (in this case it is referring to cultivars/forms i.e.Nana - not coming true from seed).
If you look at the link provided here you will note that S.japonica does indeed produce seed - enough to be a serious ecological threat in some locations in the USA.
Perhaps you have just been lucky not to have found any seed this time!
;-)

Here is a link that might be useful: Plant Conservation Alliance, Alien Plant Working Group.

Ok I am confused I dont know what kind I have now! I know one of them is Little Princess ,1 is Bridal Bouquet and the other 2 are identical except one has yellowish leaves and the other has a darker green leaf,I bought them all at Lowes!Do what I have classify as japonica?Thanks!~Angie :)

Little Princess is a variety of S. japonica. On checking the Lowe's plant guide they don't have Bridal Bouquet, however do have Bridal Wreath which they describe as S. reevesiana. They also have Double Bridal Wreath (S. prunifolia), I wouldn't worry unduly about your Little Princess being a Japonica - as a cultivar it's unlikely to be harmful in terms of being an ecological threat.
See the plant ident' link for Lowe's

Here is a link that might be useful: Lowe's plant guide search

Thanks so much for the link I had no clue it exsisted! :) I was mistaken on the "bridal bouquet",I am helping a friend plan her wedding and I have bouquets on the brain right now :),it is a "bridal wreath"! I believe it is the double! Thanks alot for the info I really appreciate it! :) ~Angie

Why not root some cuttings?

Here is a link that might be useful: Rooting guide (listing spirea)