Tetramolopium arenarium subsp. arenarium is an upright (erect) shrub, reaching a height of 0.8–1.3 meters, and is covered with tiny glands and straight hairs. The leaves are simple and alternate. The blades are lanceolate, oblanceolate, or oblong, with an acute apex and entire margins. These lance-shaped leaves measure 15 to 37 mm long and 3 to 9 mm in width. It produces five to eleven heads grouped at the end of each stem. Each head is comprised of a bell-shaped structure with 20 to 34 bracts, 2.5 to 5 mm high and 4 to 9 mm in diameter, beneath the flowers. The flowers consist of a single series of 22 to 45 white male ray florets, each 1.3 to 2.2 mm long, and 4 to 9 bisexual disk florets with maroon petals measuring 3.1 to 4.4 mm long. The fruit is a simple, dry achene (cypsela), strigose, and glandular to densely glandular, measuring 4 to 6 mm long and 0.5 to 0.8 mm wide. It occurs in dry shrublands and forests, particularly on old lava flows between 1,362 – 1,762 meters.
Bean-shaped (Reniform): Resembling the shape of a kidney or bean.
Square or Oblong: Angular shape with all sides more or less equal or longer than wide.
Triangular: Three-sided shape, broadest below the middle.
Elliptic: Rounded at both ends. shaped like an ellipse or oval.
Ovate or Obovate: egg-shaped, broader at one end.
Linear: Extremely long and narrow, with sides usually parallel.
Round: Appears circular, with length and width roughly the same.
Cardioid (Heart-Shaped): One edge has a prominent double curve into two lobes.
Cylindrical: A cylinder with parallel sides and a circular cross-section.
Discoid: Resembling a disc or plate with two relatively flat surfaces.
Fusiform: Spindle-shaped, tapering at both ends.
Globose: Spherical.
Lenticular: Resembling a lens with two convex surfaces.
Ovoid: Egg-shaped.
Plano-convex: Having a flat ventral (planar) surface and a curved dorsal (convex) surface.
Polygonal: Having more than three flat faces meeting at angles.
Sectoroid: Resembling a segment of an orange with two relatively flat faces and one curved face.
Subglobose/ellipsoid: Inflated shape but less than spherical.
Trigonous: Having three faces that meet at a distinct angle; triangular in cross-section.
Endangered species (E) are species that are so rare they’re in danger of becoming extinct.
Threatened species (T) are species that are likely to become endangered within the foreseeable future throughout all or a significant portion of their range.
Species of Concern (SOC) are species about which there are some concerns regarding status and threats, but insufficient information is available to list the species under the Endangered Species Act (ESA).
Plant Extinction Prevention (PEP) is a state status for rare plants that focuses its efforts on species that have fewer than 50 remaining wild individuals.
Orthodox seeds (desiccation-tolerant): can be dried to an internal seed moisture of less than 12% water and stored at freezing temperatures.
Intermediate seeds (temperature-sensitive) tend to age faster than orthodox seeds and may have only a 5-year lifespan when stored at -20°C. They are recommended for storage at 5°C.
Recalcitrant seeds (desiccation-sensitive): cannot be stored in a conventional freezer as they cannot survive after drying and/or freezing at -20°C. They are recommended for cryopreservation storage.