Flora of North America species comparison

erect, branched, usually (0.3–)0.5–1.5(–3) m;

proximal branches often ascending.

without nodal spines (Amaranthus spinosus sometimes with paired nodal spines).

long-petiolate;

blade obovate or rhombic-obovate to elliptic proximally, sometimes lanceolate distally, 1.5–7 × 1–3.5 cm, base broadly to narrowly cuneate, margins entire, plane, apex subobtuse to acute, usually with terminal mucro.

alternate or opposite, exstipulate, usually petiolate;

blade margins entire (entire or serrulate in Iresine; entire, crispate, or erose in Amaranthus).

of pistillate flowers with long-excurrent midrib, 4–6 mm, longer than tepals, apex acuminate or mucronulate; of staminate flowers, 4 mm, equaling or longer than outer tepals, apex long-acuminate.

terminal, linear spikes to panicles, usually drooping, occasionally erect, especially when young, with few axillary clusters, uninterrupted or interrupted in proximal part of plant.

cymules arranged in spikes, panicles, thyrses, heads, glomerules, clusters, or racemes; each flower subtended by 1 bract and 2 bracteoles (latter sometimes 1 or absent in Amaranthus).

bisexual or unisexual (plants then monoecious or dioecious), hypogynous, generally small or minute;

tepals mostly (1–)4–5 or absent, distinct or connate into cups or tubes, scarious, chartaceous, membranaceous, or indurate;

stamens 2–5, filaments basally connate into cups or tubes, rarely distinct, alternating with pseudostaminodes (appendages on staminal tubes) or not, anthers 2-locular with 1 line of dehiscence or 4-locular with 2 lines of dehiscence;

ovary superior, 1-locular;

ovules 1 or, rarely, 2–many;

style 1 or absent;

stigmas 1–3(–5).

tepals 5, unequal, 2–4 mm, apex acute;

inner tepals with prominent midrib excurrent as rigid spine, apex long-acuminate or mucronulate;

stamens 5.

tepals 1.7–3.8 mm, apex acuminate, mucronulate;

style branches spreading;

stigmas 2(–3).

utricles, dry, dehiscent or not.

dark reddish brown to brown, 1–1.2 mm diam., shiny.

black, reddish brown, or brown, lenticular, subglobose or globose (rarely cylindric), usually small;

embryo peripheral, surrounding mealy perisperm.

tan to brown, occasionally reddish brown, obovoid to subglobose, 1.5–2 mm, shorter than tepals, at maturity walls thin, almost smooth or indistinctly rugose.