Species in the arum family are mostly small perennial herbs, though the family encompasses a wide variety of growth forms. Many of the species are aquatic or wetland plants, but a few grow in uplands. New England has two distinct groups of plants in this family: the aroids and the thalloids. In the aroids, the flowers are clustered tightly together on a spike (the spadix) subtended by (and sometimes concealed within) a leaf-like or colored structure called a spathe. Pollen-bearing flowers are arranged at the top of the spike and the ovule-bearing flowers are on the bottom. The petals and sepals are small and sometimes absent, but when present they collectively number 4-6 and may be fused together. There are usually 4-6 very short stamens per flower and one ovary. The ovary sits above the perianth (i.e., is superior) and is more or less embedded into the spadix. The fruit is usually fleshy, like a berry, but may sometimes be dry. The other group, the thalloids, are free-floating plants that are not differentiated into stems and leaves; instead, they have a photosynthetic thallus that floats on the water surface or is submersed below it. In these species, there is usually only one flower per plant and the flower contains both pollen-bearing and ovule-bearring parts. They have no petals or sepals, 1 or 2 pollen-bearing flowers each with one stamen and one ovary. The fruit is a specialized type of achene called a utricle. Despite their differences, these two groups are united on many features, including details of the inflorescence and DNA sequences. The thalloid species are merely highly reduced versions of the aroids.
This Family’s Genera in New England:
Visit this family in the Dichotomous Key