Arrowhead is not a true grass, despite common names and visual similarities in foliage. The term “arrowhead” is used for plants from different botanical families, none of which belong to the true grass family. This article clarifies the botanical definition of a true grass and explains why plants commonly called arrowhead are fundamentally different in structure and classification.
The Defining Characteristics of True Grasses
True grasses belong to the Poaceae family, one of the largest and most economically important plant families worldwide. All members are monocots, meaning their seeds contain only one embryonic leaf, and they share a specific set of physical features. Their stems, called culms, are typically cylindrical and hollow in the internodes but solid and jointed at the nodes where leaves attach.
The leaves are linear, usually much longer than wide, and possess parallel venation, where veins run straight down the leaf blade. Each leaf has a blade and a cylindrical sheath that wraps around the stem. A small flap of tissue called a ligule is often present at the junction of the blade and sheath, which helps prevent water or insects from entering the sheath.
True grasses have a specialized flower structure that is almost always wind-pollinated. The flowers, called florets, are minute and organized into compact clusters known as spikelets. The fruit is a caryopsis, more commonly known as a grain. True grasses also develop a densely fibrous root system that often includes rhizomes or stolons for vegetative spread, enabling them to form dense mats.
Common Plants Referred to as Arrowhead
The common name “Arrowhead” is applied to species from at least two separate plant families. The most common aquatic plant referred to as Arrowhead belongs to the genus Sagittaria, native to wetland habitats. This plant is often called “Duck Potato” or “Wapato” because of its edible tubers, and its characteristic leaf shape is the source of the common name.
The other plant frequently called Arrowhead is the popular houseplant from the genus Syngonium, often sold as the Arrowhead Vine. This tropical species, typically Syngonium podophyllum, is known for its climbing or vining growth habit. While the juvenile leaves are distinctly arrow-shaped, mature leaves can become multi-lobed.
The Sagittaria plants are classified in the Alismataceae family, while the Syngonium species belong to the Araceae family, a group that includes familiar plants like philodendrons. Neither of these families is closely related to the true grass family, Poaceae. The plants share the “arrowhead” moniker because of the deeply notched, sagittate leaf shape.
Structural Differences Between Arrowhead and Grasses
The fundamental differences between arrowhead plants and true grasses are evident across all major plant structures, from leaves to stems and reproductive parts. True grasses have long, narrow leaves with parallel venation, a characteristic that helps them recover from grazing.
Leaf Structure and Venation
In contrast, aquatic Sagittaria species exhibit broad, deeply lobed leaves that are distinctly arrow-shaped. The houseplant Syngonium also possesses sagittate leaves in its juvenile form. Crucially, the venation in both Sagittaria and Syngonium is netted or reticulate, where veins branch out and connect in a web-like pattern. This is completely unlike the parallel arrangement found in true grasses.
Stem Structure
The stem structure provides another clear botanical separation. True grasses are defined by their hollow or jointed culms, supported by a solid node at each joint. Arrowhead plants possess solid, fleshy stems or, in the case of Syngonium, a vining stem structure that produces aerial roots for climbing. For Sagittaria, the leaves emerge from the base on long, solid leaf stalks, known as petioles, which support the leaf blade. These petioles are not the jointed culms typical of the Poaceae family.
Reproductive Differences
The reproductive organs of arrowhead plants are far more conspicuous than the reduced spikelets of true grasses. Sagittaria produces showy, insect-pollinated white flowers with three distinct petals arranged in whorls on a stalk. Syngonium, when flowering in its native habitat, produces the characteristic structure of the Araceae family: a spathe surrounding a central fleshy spike called a spadix. This elaborate floral arrangement is vastly different from the simple, wind-pollinated flowers of true grasses.
Arrowhead’s True Taxonomic Placement and Habitat
The genus Sagittaria is placed within the Alismataceae family, part of the order Alismatales, an ancient lineage of flowering plants associated with aquatic environments. Sagittaria species are obligate wetland plants, typically found in marshes, ponds, and slow-moving water bodies. They play an important ecological role as food sources for muskrats and waterfowl and are considered indicator species for healthy wetland systems.
The other common arrowhead plant, Syngonium, belongs to the Araceae family, which falls under the order Alismatales. These plants are native to tropical rainforests where they grow as epiphytes, climbing up trees using aerial roots. Syngonium is often cultivated indoors due to its tolerance for low light. The classification of both Sagittaria and Syngonium into these distinct orders confirms their botanical separation from the Poaceae family, which belongs to the order Poales.