Figure 2. Cycad phylogeny and distribution. a. Chronogram of 339 extant cycad species inferred from 100 nuclear single-copy genes, modified from Liu et al. (2022) illustrating the two extant families: Cycadaceae (Cycas ) and Zamiaceae (Bowenia, Ceratozamia, Dioon, Encephalartos, Lepidozamia, Macrozamia, Microcycas, Stangeriaand Zamia ) b. Map showing the extant distribution of cycad genera with their respective species number (blue shadow area):Ceratozamia and Dioon (Mexico and Central America);Zamia (North America to Northern South America),Microcycas (Western Cuba), Encephalartos (Africa),Stangeria (South Africa), Cycas (Asia, Indo-pacific, Africa and Madagascar), Lepidozamia , Macrozamia andBowenia (Australia). Sampled fossil localities designated with crosses, redrawn with permission from Coiro et al . (2023).
Pollination and herbivory
Like other land plants, cycads’ interactions with animals (mostly insects) include parasitic and mutualistic relationships that are largely mediated by the plants’ chemical and morphological characteristics. But cycads’ deep evolutionary history, thermogenesis, unique chemistries, and defensive traits make them somewhat unusual in the context of plant-insect interactions. These traits position cycads as especially promising for understanding a suite of ‘big questions’ in plant-insect interactions, relating to the evolutionary origins of insect pollination and phytophagy, the origins and maintenance of phytochemical diversity, insect counter-adaptations to plant defenses, and plant signaling and communication.