Flora of Tropical East Africa - Eriocaulaceae (1997)

Sylvia Phillips

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000162431
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Horticulture
• Index: Biological Sciences

The Flora is prepared at the Royal Botanic Gardens, Kew in close collaboration with East African Herbarium and in liaison with the University of Dar es Salaam, the University of Nairobi and the Makerere University. Significant contributions are also made by specialists elsewhere. This reference should be of use to anyone concerned with the identification and utilization of plants in eastern Africa.

FLORA OF TROPICAL EAST AFRICA
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ERIOCAULACEAE

SYLVIA PHILLIPS

Annual or perennial herbs usually under 1 m. high, often much smaller; stem usually abbreviated to a basal disc, infrequently elongate. Leaves narrow, lanceolate to filiform, spirally arranged, crowded into a basal rosette or rarely dispersed on elongate stems, opaque to translucent, sometimes fenestrate. Inflorescence capitate, single or in umbels, on leafless ribbed scapes. Capitula composed of many small (often tiny) unisexual flowers on a central receptacle surrounded by 1–several whorls of involucral bracts, monoecious, each flower often subtended by a floral bract. Flowers trimerous or less often dimerous, subactinomorphic to strongly zygomorphic. Perianth usually composed of two distinct whorls, sometimes reduced or absent; calyx of free, partially or almost completely connate sepals, sometimes spathe-like especially in the male flowers; petals free or partially connate, spathulate to filiform, frequently hairy, often with a subapical black gland; male petals often fused with the floral axis to form an infundibular structure topped by very small free lobes. Male flowers with stamens as many or twice as many as the sepals; inner whorl epipetalous; a vestigial gynoecium usually present. Female flowers with a superior 2–3-locular ovary; style simple, tipped with 2, 3 or 6 elongate stigmas. Fruit a thin-walled, loculicidally dehiscent capsule, each locule containing a single seed.

10 genera throughout the tropics and subtropics in marshy or seasonally inundated places, especially in montane areas on sandy soils, rarely truly aquatic; a few species of Eriocaulon also in temperate areas. The greatest concentration of genera and species is found in upland parts of South America; Eriocaulon is the only genus in Asia.

The family is easily recognisable by its capitula of small crowded flowers, atop leafless scapes and surrounded by involucral bracts. The capitula are reminiscent of Compositae but, unlike that family, are never brightly coloured, occurring in shades of white, dirty grey, brown or black.

Stamens twice as many as the petals, 6 or 4; petals usually with a black subapical gland:
Petals of female flowers free; leaves, scapes and sheaths usually glabrous	1. Eriocaulon
Petals of female flowers connate into a tube except at the base; leaves, scapes and sheaths usually hairy	2. Mesanthemum
Stamens as many as the petals, 3; petals usually eglandular:
Petals of female flowers connate in the middle, the bases and tips free; leaves, scapes and sheaths usually hairy and often glandular	3. Syngonanthus
Petals of female flowers free:
Leaves, scapes and sheaths glabrous; petals of male flowers with distinct free lobes	1. Eriocaulon
Leaves, scapes and sheaths hairy; petals of male flowers connate into a truncate tube lacking free lobes	4. Paepalanthus

1. ERIOCAULON

L., Sp. Pl.: 87 (1753) & Gen. Pl., ed. 5: 38 (1754); N.E. Br. in F.T.A. 8: 231–259 (1901); Ruhland in E.P. 4, 30: 30–117 (1903); H. Hess in Ber. Schweiz. Bot. Ges. 65: 123–178 (1955); Meikle in EW.T.A., ed. 2, 3: 57–64 (1968); Oberm. in F.S.A. 4(2): 9–19 (1985)

Scapes single, often twisted, enclosed at the base by a tubular sheath. Involucra1 bracts of the capitulum scarious to coriaceous, spreading or reflexed at maturity; floral bracts frequently white-hairy towards the tip. Flowers sessile or pedicellate on the central receptacle, male and female mixed or the female around the periphery (especially in annuals). Sepals free or ± connate especially in the male flowers, usually free in the female, often navicular, sometimes winged. Petals with a subapical or apical black gland on the inner face, or the glands sometimes reduced or absent, often white-hairy at the tip; male petals all very small or one enlarged and exserted from the capitulum. Stamens twice as many as the petals (except E. angustibracteum); anthers black or white. Seeds relatively large, ellipsoid, yellow to reddish brown, smooth or distinctively patterned.

About 400 species worldwide in tropical and subtropical regions; one species in temperate eastern U.S.A. and western Europe. The exact number of species is very uncertain, but speciation is well developed throughout the whole range of the genus.

Identification of most Eriocaulon species is not easy due to the very small size of the flowers, which nevertheless exhibit a wide range of important differences. Frequently species of extremely similar external appearance have widely different floral morphology. Only with a few of the most distinctive species is it safe to name a specimen without first dissecting the capitulum and examining the flowers. This particularly applies to the small ephemerals, often with black glabrous capitula, which spring up around the margins of drying pools and runoffs. Several species often grow together in these locations and care must be taken to avoid mixed gatherings.

The flowers easily hydrate in a drop of water for dissection, without the need for boiling. Measurements of floral parts are taken from hydrated flowers. Other measurements refer to dried material; leaves and scapes often shrink considerably on drying. It is important where possible to examine mature capitula, as the dimensions of the floral parts can alter drastically at maturity; in particular in strongly zygomorphic flowers the longest petals elongate rapidly at anthesis in the male flowers and when seed is ripe in the female, and also wings on the sepals increase in size. Leaves usually taper to some extent from the sheathing base to the tip and width measurements are taken about halfway up. Various types of hairs occur on the floral parts, and short, thick, obtuse, very opaque white hairs are widespread. Parts bearing such hairs are described here as white-papillose when the hairs are short, or white-pilose or white-villous when they are longer.

The patterning of the seed coat is of great importance in Eriocaulon, both for identification and for establishing relationships. Sometimes species with almost identical floral morphology have very different seeds. Seed-set can be sparse in the robust perennials, but otherwise seed is usually abundantly produced and is available for inspection. Although a high magnification is needed to see fine detail, the coarse patterning can be discerned with a hand lens, and this is often sufficient to confirm an identification.

Plant with a long stem clothed in numerous filiform leaves; submerged aquatic, only the capitula emergent	1. E. setaceum
Plant tufted, the leaves in a basal rosette; marsh plants or ruderals:
Anthers white; petals absent in female flowers; sepals in female flowers 0–3, filiform, caducous; slender annual	2. E. cinereum
Anthers black:
Petals absent in female flowers; sepals in female flowers 2, linear-falcate (fig. 1/8)	3. E. polhillii
Petals present in female flowers:
Flowers with 2 petals, 4 anthers and 2 stigmas:
Scapes conspicuously papillose; capitula 1–2 mm. diameter	4. E. glandulosum
Scapes smooth; capitula 1.5–4.5 mm. diameter:
Seeds uniformly brown; sepals of female flowers narrowly to very broadly winged (fig. 3/7)	5. E. mutatum
Seeds brown with a white-reticulate patterning (fig. 4/2); sepals of female flowers with a wing not wider than the sepal-body	6. E. nigrocapitatum
Flowers with 3 petals, (3–)6 anthers and 3 stigmas:
Flowers with 2 sepals and 3 petals; capitula shiny white; small annual with longitudinally ridged seeds	7. E. truncatum
Flowers with 3 sepals and 3 petals (2 broadly winged sepals in female flowers of E. strictum):
Perennials from a short rhizome, often robust capitula 8–20 mm. diameter, densely whitehairy:
Leaves not usually exceeding 20 cm. long, often much shorter, 1–5 mm. wide; scapes 4–8- ribbed; capitula 8–12 mm. diameter:
Sepals of female flowers connate into a spathe leaves acute	8. E. pictum
Sepals of female flowers free; leaves tipped by a pore	9. E. teusczii
Leaves large, thick, up to 40 cm. long and 4–18 mm. wide; scapes stout, 8–10-ribbed; capitula 9–20 mm. diameter:
Receptacle villous; female sepals villous around keel with long hyaline hairs; involucral bracts clearly shorter than capitulum width, neatly imbricate	10. E. iringense
Receptacle glabrous or thinly and inconspicuously pilose; female sepals lacking long hyaline hairs; involucral bracts as wide as capitulum or only slightly shorter:
Female sepals glabrous inside, sometimes connate and spathe-like (fig. 2/9); receptacle glabrous; involucral bracts slightly shorter than capitulum width, coriaceous at least towards base	11. E. schimperi
Female sepals bearded inside (fig. 2/8); receptacle pilose; involucral bracts as wide as capitulum, scarious	12. E. mesanthemoides
Small ephemerals, annuals or occasionally perennial (but then capitula < 7 mm. diameter or leaves < 8 cm. long); capitula 1.5–9 mm. diameter, glabrous or hairy:
Capitula subsessile, the scapes not exceeding the leaf-rosette; dwarf montane species from above 3000 m.	13. E. volkensii
Capitula rising ...

Table of contents

• Cover
• Title Page
• Copyright Page
• Eriocaulaceae
• Index to Eriocaulaceae