Acaciella angustissima
Acaciella
fern acacia, prairie acacia, whiteball acacia
erect [to spreading], glabrous or pubescent;
twigs terete to angulate, straight, short-shoots absent.
10–210 mm;
stipules linear, to 6.5 mm, margins ciliate;
petiole 3.5–65 mm, glabrous or appressed-pubescent to pilose;
pinnae 2–17[–32] pairs, 6–50[–105] mm;
rachis 5–200 mm;
leaflets 7–85 pairs per pinna, blades linear, 2–3.5[–4] × 0.5–1.3 mm, base oblique and obtuse, only midvein prominent abaxially, apex broadly acute to obtuse.
alternate, even-bipinnate;
stipules present, caducous or persistent, herbaceous; petiolate, petiole channeled;
pinnae 1–32 pairs, mostly opposite;
leaflets 2–numerous pairs per pinna, opposite, sessile or subsessile, blade margins entire, surfaces glabrous [pubescent].
usually solitary, rarely 2 or 3, axillary or terminal, pseudoracemes or pseudopanicles, to 280 mm, 9–18 mm diam.;
pedicels present.
[4–]10–40[–50]-flowered, terminal or axillary, heads, globose to slightly elongated, solitary or clustered, sometimes in pseudoracemes or pseudopanicles;
bracts present.
5–21 mm.
calyx 0.6–1.2 mm;
corolla 1.9–4.5 mm;
filaments 3–7.6 mm.
mimosoid;
calyx campanulate, lobes 5;
corolla greenish white, drying pale pink, lobes 5;
stamens 175–250, distinct, exserted, creamy white [yellow, pink];
anthers dorsifixed, eglandular;
ovary short-stipitate, glabrous;
style and stigma filiform.
legumes, stipitate, flattened, straight, linear [oblong], usually dehiscent along sutures, glabrous.
25–90 × 5.5–17 mm, rarely constricted between seeds.
3–15[–20], uniseriate, strongly flattened, ovate to orbiculate, not surrounded by pulp;
pleurogram U-shaped.
= 13.
Acaciella angustissima
Acaciella
Varieties 3 (2 in the flora).
Acaciella angustissima is the most widespread and morphologically variable species of Acaciella. Segregate species, subspecies, varieties, and forms have been recognized based on habit, leaflet shape, stem and leaflet indument, stem striations, number of pinnae, and leaflets per pinna. Acaciella angustissima is common in disturbed habitats, particularly roadsides and pastures, and it is becoming common throughout much of the tropical and subtropical regions where it was introduced originally as a forage crop. With a geographic range that extends from the southern and central United States to northern Argentina, A. angustissima is highly variable in many characteristics, one of the most obvious being plant size, which ranges from subshrubs that are sometimes nearly herbaceous, to trees exceeding ten meters. M. L. Rico-Arce and S. Bachman (2006) recognized three varieties and indicated that all three occur in North America north of Mexico. The two varieties described here are common in the central and southwestern United States. No specimens of the third variety [var. filicioides (Cavanilles) L. Rico] in the flora area have been located.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 15 (2 in the flora).
Acaciella has only recently come into common use following the division of Acacia in the broad sense into several genera, based on molecular studies (J. T. Miller and R. J. Bayer 2000; S. Gómez-Acevedo et al. 2010) and a revision by M. L. Rico-Arce and S. Bachman (2006). The following characteristics separate this genus from other members of Acacia in the broad sense (Acacia, Mariosousa, Senegalia, and Vachellia): absence of prickles and stipular spines, absence of petiolar and rachis nectaries, relatively numerous stamens (175–200+ per flower), and stalked flowers (usually in globose heads).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaflets (20–)23–40 pairs per pinna; pinna 9–17 pairs; stems white-puberulent or yellow-hirsute. | var. angustissima |
1. Leaflets 7–20(–22) pairs per pinna; pinnae 2–6(or 9) pairs; stems glabrous. | var. texensis |
1. Leaflet blades 2–3.5(–4) × 0.5–1.3 mm, only midveins prominent abaxially. | A. angustissima |
1. Leaflet blades 4–13 × 1.5–3.1 mm, lateral veins and midveins prominent abaxially. | A. lemmonii |
WildflowerSearch
iNaturalist
USDA Plants Database
