Born of dragonseed or seeds is a term to describe some bastards of House Targaryen as well as House Velaryon.
The custom of the first night had been greatly resented in the Seven Kingdoms. However, it was less protested on Dragonstone, where the Targaryens had ruled for centuries, because there the common folk viewed their beautiful, foreign rulers almost as gods. When a Lord of Dragonstone took his rights according to the first night custom, the brides were seen as "blessed", and the children born of such unions were often given lavish gifts by their father. These bastards were born of "dragonseed", and in time, became known as "seeds".
Though the right of the first night ended when it was outlawed by King Jaehaerys I Targaryen, some Targaryens continued to carry on relationships with the daughters of innkeeps and the wives of fishermen. Seeds and the sons of seeds thus remained plentiful on Dragonstone and surrounding areas, and there were many on Dragonstone who could rightly claim — or at least suspect — that some Targaryen blood ran in their veins.
The Dance of the Dragons
During the civil war known as the Dance of the Dragons, Prince Jacaerys Velaryon realised that his mother Queen Rhaenyra Targaryen's faction, the blacks, had many dragons but was in need of dragonriders. He offered lands, riches, and knighthood to any such man that could master a dragon; his sons would be ennobled, his daughters wed to lords. According to The Testimony of Mushroom, the eponymous fool had prompted Jacaerys to do so.
Jacaerys's offer gained the attention of more than just dragonseeds. Most candidates failed and were either killed or burned by the dragons. (These included Rhaenyra's Lord Commander Ser Steffon Darklyn, and Lord Gormon Massey.) Grand Maester Munkun dubbed this event "the Sowing of the Seeds", whilst others "the Red Sowing".
It is unconfirmed if the successful candidates truly had Targaryen blood, or if they did, if that ancestry is what allowed them to master the dragons. But whatever their origin in truth, the successful baseborn dragonriders were referred to as dragonseeds for the remainder of the war and within historical records.
After the betrayal of Hugh Hammer and Ulf the White at the First Battle of Tumbleton, Queen Rhaenyra and most of her council believed none of the other dragonseeds could be trusted, and ordered their arrest. Addam Velaryon escaped upon his dragon Seasmoke, but later proved his loyalty at the Second Battle of Tumbleton. In the case of Nettles, it was not only arrest that was ordered, but also execution, because she had become the lover of Rhaenyra's husband Daemon Targaryen; however, the girl fled upon Sheepstealer and was never seen again "at court or castle".
- Hugh Hammer, a blacksmith's bastard, bonded with Vermithor.
- Ulf the White, a man-at-arms, bonded with Silverwing.
- Addam of Hull, bonded with Seasmoke. Was legitimized as Addam Velaryon and made heir to Driftmark shortly thereafter.
- Alyn of Hull, the younger brother of Addam of Hull. Unable to find Grey Ghost, rejected by Sheepstealer, but legitimized as Alyn Velaryon nevertheless.
- Nettles, bonded with Sheepstealer by feeding it sheep each morning.
- Silver Denys, claimed to have been descended from a bastard son of King Maegor I Targaryen. Had an arm torn off by Sheepstealer, and was devoured with his sons by the Cannibal while trying to staunch his wound.