Letters to the twenty-first century botanist. Second series: “what is a seed?”–3. How did we get there? Palaeobotany sheds light on the emergence of seed

Abstract

This paper discusses the main steps leading to the acquisition, during the Palaeozoic, of the seed habit. The earliest spermatophytes originated in the Late Devonian and produced small cupulate ovules characterized by an elaborated sporangial apex involved in pollination. The diversification of ovules during the Carboniferous led to a wider range of sizes and shapes, and an increasing importance of the integument. The earliest seeds containing embryos are reported in Carboniferous coniferophytes.