Bull kelp sorus tissue develops on the blades that grow from the pneumatocyst, the bulb-like floating structure at the end of the stipe. The sorus tissue develops in well-defined patches on the blade, and there are often multiple sorus patches per blade. The patches develop from the tip of the blade down in the water column back towards the pneumatocyst. When they’re mature, the patches of sorus tissue will pop out of the blades like stickers or cut outs. The mature sorus tissue has  a chocolate-brown color. 

Bull kelp sorus tissue can typically be found from June to November, though sometimes it’s possible to find year round. Often the sorus patches can be collected from the surface at low tide using a small boat or skiff.

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