Tropicos | Name - Isertia Schreb.

Isertia Schreb.

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Project Name Data (Last Modified On 12/11/2023)

Acceptance : Accepted

Note : Tribe Isertieae

Project Data (Last Modified On 9/15/2020)

Notes:

Isertia includes 15 species of tropical shrubs and small trees found in Central and South America. These species are characterized by generally opposite leaves with stipules that are deeply divided in the interpetiolar part, so they appear variously intrapetiolar or as four separate stipules; terminal dichasial inflorescences branched to several orders; the flowers generally 5-6-merous; the fruits fleshy with 2-7 locules each with numerous seeds on axile placentas; and anthers that are locellate, that is, divided into a longitudinal chain of separate small chambers. Locellate anthers are found in only a few genera of Rubiaceae. The flowers of Isertia species are most often yellow to orange or red and diurnal, however several species have white, apparently nocturnal flowers. The plants are usually showy in flower, and found in secondary vegetation and rather frequently encountered by collectors. The stem apices, especially of non-reproductive stems or perhaps plants, are often markedly resinous.

Isertia is unusual in Rubiaceae in the variation it includes in corolla aestivation and fruit type. The corollas of the species of Sect. Cassupa have the lobes valvate in bud, while those of the species of Sect. Isertia are imbricated. The fruit of the species of Sect. Cassupa are are berry-like, that is, fleshy throughout with the seeds embedded in this fleshy; the fruits of the species of Sect. Isertia are drupaceous, with the endocarp or interior wall of the ovary hardened and the numerous seeds borne loosely inside these structures. The locellate anthers are unusual in Rubiaceae, and together with the deeply divided stipules show the relationship of these species.

Isertia is similar to some species of Palicourea, and these are occasionally confused. Palicourea can be separated by its ovaries with 1 ovule per locule and its drupaceous fruits that contain two or rarely three to five pyrenes, with each pyrene contaning only a single seed.

Boom (1984) studied this genus and recognized two sections. Sect. Isertia includes 8 species with drupaceous fruits and (4)5-6(7) ovary and fruit locules; Sect. Cassupa includes 6 species with berry-like fruits and 2-3 ovary locules. The species of Sect. Cassupa have sometimes been separated in the genus Cassupa, but Boom found better support for combining them in Isertia. Sect. Isertia includes I. coccinea, I. haenkeana, I. hypoleuca, I. longifolia, I. parviflora, I. rosea, I. spiciformis, and I. wilhelminensis. Sect. Cassupa includes I. krausei, I. laevis, I. pittieri, I. reticulata, I. scorpioides, and I. verrucosa.

In 1931 Standley separated the genus Creatantha from Isertia based on its corollas with the funnelform-campanulate tube "extraordinarily broad" and shorter than the thickened lobes, vs. the tube slender, cylindrical, and longer than the lobes in Isertia; he noted also that Creatantha also had the stamens inserted near the base of the corolla tube rather than in its upper part as in Isertia. Shortly afterward, in his Rubiaceae flora of Peru, Standley (1936) noted that further study showed that the type specimen of Creatantha had two flower forms, one similar to that found in Isertia and the other, which characterized Creatantha, apparently malformed or teratological and he concluded that this specimen is a diseased plant of I. laevis. Then in 1987 Steyermark separated the genus Yutajea from Isertia based on its stamens inserted near the base of the corolla tube and with the anthers basifixed, as in the holotype specimen. However Andersson (1996) studied a different specimen and found the stamens inserted at the top of the corolla, and based on a cladistic morphological analysis, he concluded that Yutajea was based on a specimen probably with teratological flowers that were damaged by beetle larvae. As noted by Andersson, occasional flowers are found in various species of Isertia with the corolla lobe abnormally wide and short, as in the flowers of Yutajea, and the corolla lobes irregularly developed in both size and shape due to insect or other damage. These flowers are also often markedly irregular rather than symmetrical; the figure that Steyermark presented in the original description of Yutajea shows them to be more regular or actinomorphic than the flowers on the holotype specimen actually are. Taylor et al. (2004) concluded that the type specimen of Yutajea is a diseased plant of I. parviflora.

Author: C.M. Taylor.
The content of this web page was last revised on 15 September 2020.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

Distribution:

Neotropics: Guatemala and Cuba to Bolivia and east-central Brazil, most species in the lowlands of South America but a few in montane forests of the central Andes.

References:

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Trees and shrubs, unarmed, terrestrial, without raphides in the tissues. Leaves opposite or ternate, petiolate, entire, with higher-order venation not lineolate, without domatia, sometimes densely white-pubescent abaxially; stipules variously interpetiolar, deeply bilobed to form apparently 4 free triangular stipules, of intrapetiolar and shortly to deeply bilobed, triangular to ligulate, generally imbricated or valvate in bud, persistent. Inflorescences terminal, thyrsoid-paniculiform or thyrsiform-racemiform, multiflowered with secondary axes terminating in dichasial or scorpioid cymes, pedunculate, bracts developed. Flowers sessile or pedicellate and bibracteolate, bisexual, homostylous, protandrous, fragrant, diurnal or perhaps sometimes nocturnal; hypanthium subglobose; calyx limb reduced or truncate and 4--6-lobed, without calycophylls; corolla salverform or tubular-funnelform with generally slender well developed tube, white to yellow, orange, or red, internally glabrous except often villous on throat and lobes, lobes 5 or 6(7), triangular, valvate or imbricate in bud, often with verrucose or protruding sinuses, without appendages; stamens 4--7, inserted in upper part of corolla tube, anthers narrowly oblong, dorsifixed, locellate (i.e., internally divded into several small chambers) and opening by linear slits, with connective prolonged or apiculate apically, included or partially exserted; ovary 2--6(7)-locular, with ovules numerous in each locule, on axile placentas; stigmas 2--6(7), narrowly oblong, included or partially exserted. Fruit drupaceous or baccate, subglobose, juicy or fleshy, at maturity red to purple or purple-black, with calyx limb persistent; pyrenes (when present) 4--6, 1-locular,trigonous, containing numerous dry seeds; seeds numerous, small (ca. 0.6--1.1 mm), irregularly angled, foveolate.

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Key To Species, adapted from Boom (1984)

1. Fruit a berry (i.e., fleshy throughout); ovary and fruit with 2-3(4) locules; stigmas 2-3(4)-lobed (Sect. Cassupa).

2. Leaf blade with white canescent pubescence or vestiture on lower surface.

3. Leaf blade bullulate, with tertiary venation impressed on upper surface.

4. Inflorescence axes glabrous or puberulous; leaf blade oblanceolate to elliptic; Andes of Peru and northern Bolivia......Isertia krausei

4'. Inflorescence axes pilosulous or hirtellous; leave blade elliptic to obovate; Andes of Bolivia......Isertia reticulata

3'. Leaf blade smooth, with tertiary venation flat or minutely raised on upper surface.

5'. Leaf blade drying membranaceous to subcoriaceous; corolla tube white, outside smooth; Central America through western South America.....Isertia laevis

5. Leaf blade drying coriaceous; corolla tube red and yellow, outside on upper part ornamented with various tubercles; Río Negro drainage, southern Venezuela and northeastern Brazil....Isertia verrucosa

2'. Leaf blade glabrescent or with strigillose to hirtellous, clear to greenish gray pubesence.

6. Corolla white, with tube 60-70 mm long, and lobes 11--20 mm long; inflorescence with secondary axes each comprising a simple 5-flowered dichasium, which terminates in 2-flowered scorpioid cymes; fruit ca. 10 mm in diameter; Colombia and Ecuador....Isertia pittieri

6'. Corolla white or yellow later turning pink, with tube 35-40 mm long and lobes 13-14 mm long; inflorescence with secondary axes each comprising a simple 9-flowered dichasium, which terminates in two 4-flowered scorpioid cymes; fruit ca. 5 mm in diameter; southwestern Costa Rica to central Panama.....Isertia scorpioides

1'. Fruit a drupe (i.e., containing individual pyenes formed from the hardened endocarp of each locule); ovary and fruit with (4)5-6(7) locules; stigmas 4-6-lobed (Sect. Isertia).

7. Stipules deeply divided in the interpetiolar portion into 2 intrapetiolar segments, these segments variously subentire to deeply lobed.

8. Leaf blades pubescent to glabrescent on lower surface; stipules 8-9 mm long; inflorescence with secondary axes each comprising a single flower, a simple 3-flowered dichasium, or a simple 5-flowered dichasium, the dichasium terminating in 2-flowered scorpioid cymes; calyx and corolla tube strigillose outside; corolla with tube orange-red and lobes yellow; northeastern Brazil and adjacent Surinam and French Guiana....Isertia spiciformis

8'. Leaf blades glabrous or glabrescent on lower surface; stipules 3-4 mm long; inflorescence with secondary axes each comprising a compound 7-11-flowered dichascium; calyx and corolla glabrous or glabrescent outside; corolla with tube pink or reddish violet and lobes pink or white; widespread in the Amazon basin.

9. Corolla with tube pink and 9-22 mm long, with lobes white; inflorescence in overall form pyramidal to cylindrical, with secondary axes each comprising a compound 5--7-flowered dichasium, which terminates in simple 3-flowered dichasia; lower (i.e., eastern portion of) Amazon basin..

10. Corolla tube 9--13 mm long..Isertia longifolia

10'. Corolla tube 17--22 mm long....Isertia psammophila

9'. Corolla with tube reddish violet and 35-50 mm long, with lobes pink; inflorescence in overall form ovoid to ellipsoid, with secondary axes each comprising a compound 11-flowered dichasium, which terminates in 2-flowered scorpioid cymes; widespread in Amazon basin but more common in upper (i.e., western) portion....Isertia rosea

7'. Stipules deeply divided, apparently four free stipules.

11. Corolla tube 43-70 mm long; fruit ca. 10 mm in diameter.

12. Leaf blade with gray to clear floccose pubescence on lower surface; inflorescence with secondary axes each comprising either a simple 3-flowered dichasium, or a compound 7-flowered dichasium that terminates in 2-flowered scorpioid cymes; northeastern Brazil and southern Surinam and French Guiana....Isertia coccinea

12'. Leaf blade with white canescent pubescence on lower surface; inflorescence with secondary axes each comprising a simple 7-flowered dichasium, which terminates in two 3-flowered scorpioid cymes; widespread in northern Amazon basin....Isertia hypoleuca

11'. Corolla tube 5-30 mm long; fruit 4-8 mm in diameter.

13. Corolla tube pink, 5-13 mm long; inflorescence with secondary axes each comprising a compound dichasium of ca. 31 flowers....Isertia parviflora

13'. Corolla tube red, orange, or yellow, 24-30 mm long; inflorescences with secondary axes comprising a simple or compound dichasium of 8-18 flowers.

14. Leaf blades smooth, with tertiary venation not prominent, at base acute and decurrent along petiole; inflorescence with secondary axes comprising a simple 8-18-flowered dichasium, which terminates in scorpioid cymes of 4-9 flowers; Cuba, Central America, northern Colombia, and northern Venezuela.....Isertia haenkeana

14'. Leaf blades rugose, with tertiary venation prominent on upper and lower surfaces, at base rounded to acute, not decurrent along petiole; inflorescence with secondary axes comprising a compound 11-flowered dichasium, which terminates in 2-flowered scorpioid cymes; sandstone table mountains of southern Surinam and adjacent Brazil......Isertia wilhelminensis