Named forms of woody garden plants often do not come very true from seed anyway

Is the seller from China? I have seen many people buy seed from China only to be duped. Buyer beware. There are some unscrupulous sellers in the states too but not as bad.

I just did an image search for hydrangea seed and some of those are from AliExpress which look very suspect.

https://www.aliexpress.com/i/4000145701547.html

Here is a site that looked more promising on seed size.

https://plantaddicts.com/growing-hydrangeas-from-seed/

Collect the seeds from your own hydrangeas (mopheads will be more difficult as they have less fertile flowers and therefore less seeds). Fall or later is the best time for this. They have 1/4 to 5/16 of an inch, conical to urn shaped, seed containing capsules that turn brown. They have a small opening in the top. The seeds inside look brown and dust like in size so hydrangea seeds are tiny compared to these huge ones.

What you see in the picture is too large. They are probably viburnum seeds instead. The packet is mislabeled.

These look a lot like the seeds many people have reported receiving in the mail--unordered. No one knows who is mailing them. But you might contact your state agricultural office. In any case, do not just throw them away or flush them.

The OP said they purchased the seeds as Hydrangea Mars. The seeds look nothing like Hydrangea seed though.

Yes, intended, purchased seeds are much different than the unsolicited, random receipt of unidentified foreign seeds. These were ordered specifically as seeds of Hydrangea macrophylla Mars (one of the Cityline series) and are clearly labeled as such. But as others have noted, they are NOT hydrangea seeds and even if they were, any resultant plants would not be true to that variety.

Probably viburnum seeds.

Definitely NOT Hydrangea seed or seed capsules.

I think that they are hypericum seed pods.

Oh God, I remember the old gardenweb forum and we used to share seeds, and someone sent me seeds of a beautiful variety of morning glory, but she didn't remember what they were. Well, stupid me, I planted them along a gate and got tons of bindweed. Literally took me years to get rid of that. LOL.

They are assuredly not Hypericum fruit which contain lots of small seeds, not a single large flat seed.

What happened, finally? Did you plant them? What were they, in the end? Thank you

They look just like the viburnum fruits that I pick from my 2 deciduous viburnums. You can see the (single) seed in one of them.