Hayarum mirispathum gen. nov. et sp. nov. A. Cultivated flowering plant, B. Inflorescence at pistillate anthesis (spathe limb strongly reflexed and curled), C.–D. Inflorescence at post pistillate anthesis (spathe limb beginning to uncurl and gradually becoming erect), E. Inflorescence at post staminate anthesis (pollen released, spathe limb closing, partly leaving the appendix visible and remaining erect, spathe base margins recurve and gaping, revealing the staminate zone), F. Detail of spadix showing pistillate zone, sterile zone, staminate zone, supra-staminal sterile zone, and base of the appendix (nearside spathe artificially removed), G. Longitudinal section of pistil with with a single erect, sessile ovule on a basal placenta. Scale bars: A=2 cm, B–E=1 cm, F=5 mm.  Photos by D. Prehsler.

Hayarum K.Z.Hein, Prehsler, Saensouk & S.L.Low, gen. nov. 

Diagnosis: Hayarum, with its sole species H. mirispathum, is uniquely defined by the combination of its remarkable spathe movement during anthesis, a pistillate zone of the spadix free from the spathe, a short sterile zone between the pistillate and staminate zones which is completely covered with a single whorl of subglobose staminodes, a staminate zone wholly contained within the spathe base and a unilocular ovary with a single erect, sessile ovule on a basal placenta. Hayarum shares certain morphological features with the genus Pinellia, notably the unilocular ovary with a single erect, sessile ovule on a basal placenta, and the gaping of spathe base margins during late staminate anthesis. However, in Pinellia, the spathe is mostly with a transverse septum between the pistillate and staminate zone, and its pistillate zone is adnate to the spathe. In contrast, Hayarum lacks this transverse septum and its pistillate zone is entirely free from the spathe. The inflorescence of Hayarum resembles that of the genus Typhonium, but the latter differs by having non-opening spathe base throughout anthesis, ovaries with a single ovule held obliquely on a funicle on a basal placenta, and a staminate zone which is completely exserted from the spathe base. 

Etymology: The generic name Hayarum honors British botanist Alistair Hay (+ ‘arum’, from the Greek αρου, an ancient name for Arum). Alistair Hay is an expert on Asian Araceae and the former Director of the Sydney Botanical Garden in Australia. In recognition of his outstanding contributions to aroid research, he was awarded the H.C. Schott Award for excellence in aroid research in 2023. Hay is regarded as the world authority on the subfamily Lasioideae (Araceae) and has conducted extensive research on the Malesian and Australian Araceae. He also inspired the first author (KZH) to pursue the study of aroids and has always kindly suggested and guided throughout his aroid research. 

Hayarum mirispathum K.Z.Hein, Prehsler, Saensouk & S.L.Low, sp. nov. 

Diagnosis: Hayarum mirispathum bears the closest morphological resemblance to Pinellia and Typhonium. Hayarum mirispathum differs from Pinellia in several key morphological traits. It has a pistillate zone of the spadix that is free from the spathe, a short sterile zone between the pistillate and staminate zones that is completely covered with a single whorl of staminodes, and a spadix shorter than the spathe. In contrast, Pinellia exhibits a pistillate zone adnate to the spathe, a longer prominent sterile zone between the pistillate and staminate zones that is entirely naked, and a spadix much longer than the spathe. Hayarum mirispathum differs from Typhonium, to which it bears the closest resemblance, in having gaping spathe base margins during late staminate anthesis, a unilocular ovary with a single erect, sessile ovule on a basal placenta, and a staminate zone that is fully contained within the spathe base. Typhonium possess non-gaping spathe base margins throughout anthesis, a unilocular ovary with a single obliquely positioned ovule on a funicle on a basal placenta, and a staminate zone fully exserted from the spathe base.