Paracephaelis Baill.

Block, Petra De, 2022, Monograph of the western Indian Ocean genus Paracephaelis (Rubiaceae - Pavetteae), with description of thirteen new species, European Journal of Taxonomy 801, pp. 1-99 : 19-23

Genus Paracephaelis Baill.

Adansonia 12: 316 ( Baillon 1879); Histoire des Plantes 7: 496 ( Baillon 1880); Natürliche Pflanzenfamilien 4 (4): 60 ( Schumann 1891); Notulae Systematicae 16: 7, fig. 1, 1–7 ( Arènes 1960); Systematics and Geography of Plants 73: 100 ( De Block 2003): Flora Zambesiaca, Rubiaceae 5 (3): 619 ( Bridson 2003); Taxon 64: 91 ( De Block et al. 2015).

– Type species: P. tiliacea Baill.

Homolliella Arènes, Notulae Systematicae 16: 16, fig. 4, 19–25 ( Arénes 1960); Taxon 64: 91 ( De Block et al. 2015). – Type species: Homolliella sericea Arènes.

Description

Shrubs, 1–6 m tall, or small to large trees, 4–20 m tall, dbh up to 30 cm. Pubescence whitish, tawny or reddish brown. Young shoots somewhat flattened, often bisulcate, variously pubescent or, more rarely, glabrous; older branches usually terete, glabrous or glabrescent, bark often corky, flaking or not, greyish, pale brown, fawn, brown or reddish brown. Leaves rarely deciduous, petiolate; petioles canaliculate above, 0.2–3 cm long, variously pubescent or, more rarely, glabrous; blades variously shaped, from narrowly elliptic/ovate/obovate to orbicular, (sub)coriaceous or, more rarely, papyraceous, both surfaces variously pubescent or, more rarely, glabrous; base attenuate to strongly cordate; tip acuminate with acumen 0.2–2.5 cm long, retuse, rounded, obtuse, acute and often mucronulate, or aristate; margin revolute (when dried); domatia present or absent; venation brochidodromous; midrib usually impressed (at least in the basal leaf half) or raised with a central groove (e.g., P. sambavensis sp. nov., P. sericea ) above, prominently raised below; secondary veins 3–14 on each side of midrib. Stipules interpetiolar, basally fused into a cone with upper parts free, outer surface moderately to densely pubescent, more rarely sparsely pubescent or glabrous, inner surface usually glabrous, with 1–3 rows of colleters, sometimes interspaced with long hairs, at the base; sheath triangular or, more rarely, ovate, 0.1–3 cm long, often keeled; tip acute or obtuse, or, more often, with needle-like awn up to 6 mm long. Inflorescences terminal on lateral shoots or lateral short-shoots, sometimes becoming pseudo-axillary later on ( P. tiliacea ), usually sessile but rarely shortly pedunculate ( P. longipedicellata sp. nov.), cymose, compact to lax, consisting of (1–)3 to numerous flowers; all inflorescence parts (peduncle, axes, pedicels, bracts, and bracteoles) densely pubescent with short to long, erect, spreading or appressed hairs (hairs more appressed on bracts and bracteoles when dried); in sessile inflorescences, first order bracts identical to vegetative leaf pair and stipules, with leaves identical in size to vegetative leaves, somewhat to conspicuously smaller or always fallen (resulting in a seemingly shortly pedunculate inflorescence; e.g., P. tiliacea ); central second order bracts sometimes identical to first order bracts but with reduced stipular parts and smaller leaves, or, identical to higher order bracts; higher order bracts with stipular parts reduced or absent and foliar parts triangular and vaulted, trilobed or linear, 1–10 mm long, or, more rarely, linear and leaf-like, up to 15 mm long; bracts and bracteoles moderately to densely, or rarely sparsely, covered with short appressed hairs and with a basal row of colleters or 2 basal marginal groups of 1 to few colleters inside. Flowers fragrant, sessile or pedicellate, 5-merous, hermaphrodite. Calyx usually well-developed with tube longer than lobes in species from humid vegetation types, lobes longer than tube in species from dry vegetation types, rarely tube and lobes of ± equal length, green in living condition, densely covered with short to long, erect, spreading or appressed hairs outside, inner surface often covered with appressed hairs but without colleters; tube cylindrical, 0.2–12 mm long; lobes 0.25–4(– 5 in fruiting stage) mm long, narrowly triangular, triangular, ovate, quadrangular or somewhat oblong in shape, bases not overlapping, tips acute, obtuse, rounded or acuminate; tube and/or lobes sometimes accrescent in fruiting stage. Corolla white, turning yellowish with age, densely covered with ± long appressed (or rarely somewhat spreading) hairs outside, at least partly pubescent inside, throat glabrous; tube narrowly cylindrical, 3.5–33 mm long, longer than or, more rarely, equal to lobes in length; lobes contorted to the left in bud and spreading at anthesis, oblong, 1.2–9 mm long, inner surface glabrous, tips blunt. Stamens inserted in the sinuses of the corolla lobes at or, rarely, somewhat below the level of the throat ( P. longipedicellata sp. nov.); anthers completely exserted or basalmost 1–2.5 mm included in corolla tube at anthesis, linear, 1.2–8 mm long, basi- or basimedifixed, sagittate, with short sterile apical appendix to ca 0.5 mm long; filaments 0–2.5 mm long. Disc annular, fleshy, glabrous. Ovary cupular, bilocular, 0.7–3 mm long, green in living condition, often longitudinally ribbed when dried, densely pubescent. Placentation axile; placenta attached to middle or upper half of septum; (1–)3–14 ovules arranged at periphery of large placenta, or, 1–5 ovules pendulous from small placenta. Style and stigma white; style slender, moderately to densely covered with erect or ascending hairs on its upper half; stigma at least partly exserted at anthesis, stigmatic lobes fused over their entire length, usually not much thickened or at most (upper part) slenderly fusiform, only the very tips spreading, papillae located in the lines of fusion of the stigmatic lobes, papillate grooves 2.5–16 mm long. Fruits drupaceous, spherical to ovoid, longitudinally ribbed or not (when dried), moderately to densely covered with short to long, erect, spreading or appressed hairs; calyx persistent; mesocarp thin or well-developed, vascular bundles sclerified; pyrenes 2, hemi-ovoid or hemispherical, usually crustaceous, with rounded or truncate base, rounded, acute or acuminate tip, and small adaxial opening; larger pyrenes with longitudinal central ridge running from the apex to the top of the adaxial opening, sometimes continuing into a longitudinal depression below it and pyrene opening along this longitudinal ridge and depression; smaller pyrenes without longitudinal ridge and depression, without opening mechanism; seeds laterally compressed, (1–)2–10/fruit, reddish brown or dark brown, hilar cavity shallow, elongate to linear; endosperm entire; embryo with foliaceous cotyledons, radicle inferior. Pollen grains 3-zonocolporate; exine perforate at apocolpium, perforate or rarely microreticulate at mesocolpium: supratectal microgemmae present.

Distribution and habitat

A genus with 18 species, centred in Madagascar (16 endemic species), with one species ( P. comorensis sp. nov.) endemic to the Comoros and another species ( P. trichantha ) occurring along the coast in eastern Africa and on the islands of the Aldabra Group. Occurring in both humid and dry vegetation types: humid littoral, sublittoral, low-elevation to montane forest, high plateau forest, gallery forest, dry littoral forest and dune vegetation, scrub, semi-deciduous or deciduous dry forest; on sandy (white or laterite) soil or on rocky substrate, also on limestone or limestone covered with sand; 0–1700 m a.s.l.

Notes

1. Homolle (1938: 608) published a separate section within the genus Tarenna , comprising species characterized by a reduced placenta and seeds with an elongate shallow hilum (“graines non ombiliquées”) and cited P. cinerea and P. comorensis sp. nov. as members. Unfortunately, section “ Cinerescens ” was only accompanied by a short French description, which does not constitute valid publication according to art. 39.1 of the International Code of Nomenclature for algae, fungi, and plants ( Turland et al. 2018).

2. In his unpublished Révision des Rubiacées de Madagascar et des Comores, Capuron recognized the sections “ Cinereae ” (1973: 169) and “ Paracephaelis ” (1973: 174) in his broadly circumscribed genus Tarenna . Both sections correspond to Paracephaelis as delimited here. See Taxonomic history for further information.

3. Bridson (1979: 400, 1988: 585) used the informal name Tarenna “group VI” to indicate the only continental African species of Paracephaelis , P. trichantha .

Key to the species of Paracephaelis

1. Pedicels 8–20 mm long in flowering stage; bracteoles on pedicel 1–10 mm below the ovary, not opposite; anthers ca 8 mm long, part exserted from corolla tube spirally twisted (when dried); calyx tube and lobes of ± equal length, lobes quadrangular or shortly oblong, 0.7–1.2 mm long, with rounded tips ............................................................................................ P. longipedicellata De Block sp. nov.

– Pedicels 0–3(–6) mm long in flowering stage; bracteoles at base of ovary or on pedicel just below ovary, (sub)opposite; anthers (1.5–)3–5(–7) mm long, not spirally twisted; calyx lobes much longer than calyx tube or vice versa, or, if of equal length, then either lobes (narrowly) triangular or pedicels much shorter ..................................................................................................................................... 2

2. Leaves 1–4 × 0.7–2.8 cm, grouped at the end of lateral shoots; blades elliptic, ovate, rarely obovate or orbiculate; inflorescences 0.6–1.5 × 1–2 cm; calyx tube (0.2–) 0.4–0.7 mm long, lobes triangular, 0.8–1.5 mm long .......................................................................... P. saxatilis (Scott Elliot) De Block

– Leaves up to 23× 12 cm, not consistently <4 cm long, only rarely grouped at the end of lateral shoots; blades of different shape, if as narrow as above, then> 4 cm long and/or shape narrowly obovate or narrowly elliptic; inflorescences 1–10 × 1–13 cm; usually, either calyx tube (1–12 mm) or lobes (1.5–4 mm) longer, or, if of similar length, then inflorescences much larger ................................... 3

3. Ovary + calyx ≤ 2.5 mm long (flowering stage); calyx tube + lobes ≤ 1.5 mm long; per locule 1–5 ovules pendulous from the base of a small placenta; fruits spherical, 0.3–0.6 mm in diameter................... 4

– Ovary + calyx 3–17 mm long (flowering stage); calyx tube + lobes 2–14 mm long; per locule (1–)2– 14 ovules at the periphery of a large placenta, rarely ovules restricted to top of placenta; fruits often ovoid, if spherical, then usually larger .............................................................................................. 6

4. Leaves 6–23 × (2.5–) 4–13 cm, papyraceous or subcoriaceous, both leaf surfaces glabrous or with sparse long appressed hairs on midrib and secondary veins, tip acuminate, acumen 5–25 mm long; young shoots glabrous .................................................................... P. comorensis De Block sp. nov.

– Leaves 2–13 × 1–8.5 cm, subcoriaceous or coriaceous, both leaf surfaces variously pubescent or glabrous, tip only rarely acuminate; young shoots rarely glabrous but usually pubescent .............. 5

5. Petioles 7–22 mm long; calyx lobes 0.25–0.5 mm long; corolla tubes 3.5–5.5(–6) mm long; corolla lobes 1.2–2 mm long; anthers 1.5–2 mm long, filaments 0.1–0.2 mm long ....................................... ........................................................................................................... P. trichantha (Baker) De Block

– Petioles 4–10(–15) mm long; calyx lobes 0.5–1 mm long; corolla tubes 5–7.5 mm long; corolla lobes 3–4.5 mm long; anthers 3–4 mm long, filaments ca 1 mm long ........................................................ ................................................................................................. P. cinerea (A.Rich. ex DC.) De Block

6. Upper leaf surface glabrous, sometimes with some pubescence on margin, midrib and secondary veins .................................................................................................................................................. 7

– Upper leaf surface variously pubescent (pubescence not restricted to margin, midrib and secondary veins) ............................................................................................................................................... 13

7. Calyx tube (much) longer than calyx lobes, tube 1–10 mm long, lobes 0.5–2 mm long, quadrangular, broadly ovate or triangular; tree 8–20 m tall, more rarely shrub to 5 m tall; inflorescences with numerous flowers, more rarely with 12–60 flowers ......................................................................... 8

– Calyx lobes (much) longer than calyx lobes, tube 1–1.5(– 2 in fruiting stage) mm long, lobes 1.2–3(– 5 in fruiting stage) mm long, oblong or triangular; shrub or small tree to 6 m tall; inflorescences with 3–35 flowers .....................................................................................................................................11

8. Inflorescences with 3–12 flowers; calyx tube 4–10 mm long; corolla tube 1.1–3.3 cm long ............ ............................................................ P. pauciflora De Block sp. nov. (upper leaf surface glabrous)

– Inflorescences with 12 to numerous flowers; calyx tube 1–5 mm long; corolla tube 0.6–1.7 cm long ................................................................................................................................................... 9

9. Stipules 0.8–3 cm long; calyx tube 2–5 mm long .............................................................................. ................................................................ P. sericea (Arènes) De Block (upper leaf surface glabrous)

– Stipules 0.25–0.8 cm long; calyx tube 1–2 (– 3 in fruiting stage) mm long ................................... 10

10. Leaves 4.5–10.5 × 1–4 cm; inflorescences 1.5–4 × 2–5 cm; flowers sessile; bracteoles 1.5–2 mm long; calyx tube 1.5–2 mm long in flowering stage, ca 3 mm long in fruiting stage; connective sparsely covered with appressed hairs ............................................................. P. orientalis De Block sp. nov.

– Leaves 13–18 × 5.5–8.5 cm; inflorescences 4–8 × 4–8 cm; pedicels 1–2 mm long in flowering stage, up to 5(–8) mm long in fruiting stage; bracteoles ca 1 mm long; calyx tube 1–1.5 mm long; connective unknown ....................................................................................... P. sambavensis De Block sp. nov.

11. Lower leaf surface densely covered with long, erect or spreading hairs ............................................ ................................................................................................................ P. aristata De Block sp. nov.

– Lower leaf surface glabrous, either completely or with some hairs on margin, midrib and secondary veins ................................................................................................................................................ 12

12. Young shoots and petioles glabrous; stipular awn 1–1.5 mm long; both leaf surfaces completely glabrous; bracteoles 0.7–1.2 mm long; calyx lobes 1.2–1.5 mm long ............................................... ............................................................................................................... P. gautieri De Block sp. nov.

– Young shoots and petioles densely covered with spreading or appressed hairs; stipular awn 2–4.5 mm long; margin, midrib and sometimes secondary veins sparsely to moderately pubescent on both leaf surfaces; bracteoles 2–3 mm long; calyx lobes 2.5–3 mm long ........ P. bardotiae De Block sp. nov.

13. Calyx lobes longer than calyx tube; young shoots, petioles, inflorescence axes and pedicels densely covered with long erect or spreading hairs ..................................................................................... 14

– Calyx tube longer than calyx lobes; young shoots, petioles, inflorescence axes and pedicels densely covered with short erect hairs ......................................................................................................... 16

14. Leaves not clustered at the end of lateral shoots; stipules 1–2.5 cm long; bracteoles 3–5 mm long; pedicels 0–5 mm long in flowering stage, 0–12 mm long in fruiting stage ........................................ ................................................................................................................ P. russata De Block sp. nov.

– Leaves clustered at the end of lateral shoots; stipules 3–7 mm long; bracteoles 1.5–3 mm long; pedicels 0–2 mm long ................................................................................................................................... 15

15. Terminalia -branching present; pubescence reddish brown, tawny or whitish; leaves probably deciduous, 7–20 × 5–15 cm, papyraceous or subcoriaceous; inflorescences terminal, becoming pseudo-axillary; calyx lobes (1.5–) 2–3.5 mm long ................................................... P. tiliacea Baill.

– Terminalia -branching absent; pubescence tawny or, more rarely, whitish; leaves not deciduous, 2–8.5 × 1.5–5 cm, coriaceous; inflorescences terminal; calyx lobes 1.5–2 mm long in flowering stage, up to 3.5 mm long in fruiting stage ............................................. P. seyrigii De Block sp. nov.

16. Leaves with lower surface sericeous, tips obtuse to retuse; ovary and calyx densely covered with long, spreading or erect hairs outside .............................................. P. ranirisonii De Block sp. nov.

– Leaves with lower surface densely covered with erect hairs, tips acuminate with acumen 0.3–2 cm long; ovary and calyx densely covered with short erect hairs outside ........................................... 17

17. Inflorescences capitate; flowers sessile ........................................................................................... 18

– Inflorescences not capitate; flowers sessile or shortly pedicellate, pedicels 0–2(–5) mm long ...... 19

18. Leaves often drying somewhat bullate; bracteoles 1.5–2.5 mm long, tips acute; calyx lobes with obtuse to rounded tips, not reflexed; fruits 15–20 × 10–15 mm ......................................................... ....................................................................................................... P. grandifructa De Block sp. nov.

– Leaves not drying bullate; bracteoles 3–3.5 mm long, tips acuminate; calyx lobes with acuminate and reflexed tips; fruits 10–13 × 8–10 mm ..................................... P. capitulifera De Block sp. nov.

19. Inflorescences with 3–12 flowers; stipules 0.4–0.9 cm long; calyx tubes 4–10 mm long; corolla tubes 1.1–3.3 cm long ................................................................................ P. pauciflora De Block sp. nov.

– Inflorescences with 12 to numerous flowers; stipules 0.8–3 cm long; calyx tubes 2–5 mm long; corolla tubes 0.6–1.7 cm long ........................................................................... P. sericea (Arènes) De Block