surname, hydropyrum latifalium
蔣 is a rare kanji with two distinct uses: a surname and a plant name (hydropyrum latifalium, a type of wild rice). These meanings do not share a clear conceptual center, so treat it as a character used for names and a specific plant.
蔣 combines 艹 (grass/plant) with 將, which likely contributes the sound. The plant meaning is directly tied to the grass radical, while the surname use is a phonetic loan. The exact historical development is uncertain.
The top 艹 suggests a plant, and the bottom 將 looks like a general commanding. Imagine a general standing in a field of wild rice (hydropyrum latifalium), giving orders. This plant is so distinctive it became a surname.
For ショウ, picture the general (將) showing off his wild rice field: show -> ショウ. The general shows the plant that bears his surname.