na-adjective
Describes an approach, method, or arrangement that follows a clear, logical order or system.
彼は問題を系統的に分析した。
He analyzed the problem systematically.
この教科書はとても系統的でわかりやすい。
This textbook is very systematic and easy to understand.
組織的 means 'organized' or 'systematic' with a focus on coordinated group effort or institutional structure, whereas 系統的 is more about logical order and method.
Formed from 系統 (system, lineage) + the adjectival suffix 的 (-tic). The word 系統 itself is a Sino-Japanese compound of 系 (lineage, system) and 統 (unite, govern).