This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蕐 is a rare variant of 華 (flower). The exact historical development is uncertain, but it likely shares the same origin as 華, with 艹 (grass) and a phonetic component.
The top 艹 suggests a plant, and the complex lower part resembles a blooming flower. Think of 蕐 as an ornate, old-fashioned way to write 'flower'.
For カ, imagine a rare flower blooming in a car: car -> カ, and the flower is the unusual 蕐.