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Published In: Hortus Kewensis 1: 67. 1789. (Hort. Kew.) Name publication detail
 

Project Name Data (Last Modified On 6/6/2016)
Acceptance : Accepted
Images of Iridaceae     (Last Modified On 2/4/2017)
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Taxon Profile     (Last Modified On 7/26/2016)
Description: Evergreen herbs with short to long rhizomes or aerial stolons (A. singularis). Stems rounded to compressed and 2-sided, then 2-angled or 2-winged, simple or few- to many-branched. Leaves sword-shaped to linear or terete, in two ranks, crowded basally, usually with a few progressively smaller leaves above; without marginal vein or subepidermal sclerenchyma, marginal epidermal cells thickened, columnar. Inflorescence simple or compound, composed of one or more binate rhipidia (flower-clusters in 2 series, unless reduced to 1 flower); lateral clusters stalked or sessile; spathes enclosing flowers green, rust-colored, or partly to entirely membranous or dry and papery, margins entire, irregularly torn, or fringed; floral bracts (within spathes) similar but usually smaller, forked apically, often 2-keeled. Flowers actinomorphic, upright or half to fully nodding, mostly fugaceous, lasting a single day (rarely 2 days), pedicellate or often subsessile, perianth twisting spirally on fading, persisting on ovary, usually dark blue, sometimes pale blue, white, mauve, or pink, occasionally with contrasting markings, scentless; with nectar from perigonal nectaries only in A. spiralis; tepals basally connate for 0.5–2.0(3.0) mm, subequal, or outer tepals shorter, always narrower than inner, oblanceolate to obovate, usually spreading horizontally, sometimes ascending. Stamens free; filaments filiform (unequal in A. inaequalis); anthers oblong to linear. Ovary top-shaped, triangular-columnar or oblong, with ovules opposite in 2 rows or alternating, forming a single row; style filiform, eccentric, either minutely 3-notched or divided into spreading, ± subentire or deeply fringed stigmatic lobes. Capsules ovoid to oblong or cylindric, rounded in section or shallowly to deeply 3-lobed, or broadly 3-winged, subsessile or stalked, remains of perianth persisting on developing capsule. Seeds rounded to angular (prismatic), shortly cylindric, triangular-columnar, or radially compressed and lamellate, with foveate sculpturing or smooth, many per locule or only 1 or 2. Pollen grains monosulcate, zonosulcate, trisulcate, spiraperturate, sometimes exine covering aperture, exine reticulate to microreticulate or rugose. Basic chromosome number x = 16.
Etymology: from the Greek, arista, an awn, a dry, acute-tipped bract-like structure, as in the dry, fringed spathes and bracts of the type species, Aristea africana.
Revisionary account:
General Notes: Species ± 57; 44 in southern Africa and most diverse there; extending through tropical Africa to Senegal and Ethiopia in the north, 8 in Madagascar; most frequent in well-watered highlands in grassland, rocky outcrops, or marshes; in the southern African winter-rainfall zone often montane and in rocky sandstone habitats, frequently flowering in mass after fires.

Despite relatively modest variation in floral structure, species of Aristea vary remarkably in pollen grains and fruit and seeds morphology. In subg. Eucapsulares pollen grains are mostly inaperturate or have exine covering the apertures rendering them difficult to identify; the exine usually rugose to rugulose. In subg. Aristea pollen grains are either monosulcate (rarely zonosulcate) or spiraperturate. In subg. Pseudaristea pollen grains are dizonosulculate with reticulate exine. Capsules and seeds vary from ovoid-ellipsoid to cylindric-3-lobed (sub, Eucapsulares) to broadly radially winged (sect. Racemosae). Seeds are prismatic to subglobose in many. Eucapsulares, cylindric or cylindric-triangular in subg. Pseudaristea and flattened and lamellate in most subg. Aristea. The variation in fruit and seed stucture is largely congruous with pollen variation and forms the basis for the current infrageneric taxonomy which recognizes three subgenera. This is turn corresponds broadly with preliminary molecular study.

Floral morphology is conservative, most species having blue flowers with the tepals united only basally and yellow anthers. The flowers last a single morning, deliquescing after midday. Such flowers lack nectar and are pollinated by pollen collecting female bees, Only species of subg. Pseudaristea depart from this pattern, having blue to white or pink flowers often with dark markings. Flowers of A. lugens have dark brown to almost black outer tepals. Pollination most these species is by hopliine beetles that use the flowers for assembly and mating. Flowers of A. spiralis of the subgenus secrete nectar from perigonal nectaries and are recorded as being pollinated by long-proboscid flies.

 

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1 Capsules elongate, leathery to ± woody when dry, 20–70 mm long, tardily dehiscent; ovary on pedicels 5–18(–25) mm long, cylindric-trigonous or cylindric triangular, 8–17(–22) mm long; style dividing into 3 spreading lobes each deeply fringed; pollen grains with 2 ring-like apertures (dizonasulculate) Aristea subg. Pseudaristea
+ Capsules not as above, dehiscent in upper half, 3.5–50 mm long; ovary subsessile or on pedicels short, usually < 4 mm long, obovoid, often shallowly 3-lobed; style either minutely 3-notched at apex or dividing into 3 spreading entire or shallowly fringed lobes; pollen grains various not dizonasulculate (except some A. zeyheri) (2)
2 (1) Capsules short to relatively long, 8–15(–25) mm, with 3 radial, usually narrow wings; seeds compressed radially, flattened and lamellate (except A. singularis); style either minutely 3-notched at apex or dividing into 3 spreading entire or shallowly fringed lobes Aristea subg. Aristea
+ Capsules short to elongate, usually 4–35(–50) mm, shallowly to deeply 3-lobed but lobes not forming wings; seeds columnar with flattened ends, rounded or angular; style dividing into 3 spreading entire or shallowly fringed lobes Aristea subg. Eucapsulares
 

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