Boehmeria densiflora Hook. & Arn.
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publication ID |
https://doi.org/10.3767/000651913X674116 |
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persistent identifier |
https://treatment.plazi.org/id/03D987B7-FFF4-512A-FD70-5D08DBCCFAEB |
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treatment provided by |
Felipe |
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scientific name |
Boehmeria densiflora Hook. & Arn. |
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18. Boehmeria densiflora Hook. & Arn. View in CoL — Fig. 15h–o View Fig , 16 View Fig ; Map 17 View Map 17 , 18 View Map 18
Boehmeria densiflora Hook. & Arn. (1838) 271. ― Type: Voyage of Capt. Beechey , Lay & Collie in herb. Arnott s.n. (holo E, n.v.), Japan, Ryukyu Islands [Lou-tchou Islands].
Shrub, 0.3–2(–7) m tall but often low and spreading, stem up to 1.5(–5) cm diam; ultimate branches c. 1.2 mm diam, adpressed-hairy, hairs dense, fine, giving rather greyish appearance, later glabrescent. Stipules 5–10 by 1.5–2 mm, relatively thick-textured. Leaves opposite (rarely a few alternate), (slightly to) markedly dimorphic with lamina of ‘larger’ leaves (1.1–)1.5–2.5 × length of ‘smaller’ ones and usually relatively narrower, with more tapering apex; ‘larger’ leaves usually slightly asymmetrical, ovate to linear-ovate (rarely elliptic or obovate), small or medium 6–14(–20) by (1–)1.5–6(–9) cm, length 2–5(–7) × width, margin finely-serrate, teeth 20–30(–40 on longest leaves) either side, sharply acute and shallow but markedly wide-spaced, 0.3–0.7(–1) mm long (sometimes reduced to hard mucro), tooth-apices 3–6 mm apart; leaf apex gradually tapering attenuate or very indistinctly acuminate and often sideways-curved, or acute but extreme tip abruptly long-mucronate; base shortly cuneate or narrowly rounded, often slightly asymmetrical; ‘smaller’ leaves relatively slightly broader and less tapering, narrowly to broadly acute; basal veins extending into distal third of lamina or almost to tip, upper lateral veins (1–)2–3, all arising in distal half or in distal third of lamina, indistinct adaxially, distinct and finely prominent abaxially; tertiary venation reticulate, distinct or not; texture thin- or thick-chartaceous, leaves smooth or slightly bullate, adaxial surface abundantly hairy, hairs very fine, inconspicuous, adpressed, giving a slightly rough feel, cystoliths large, prominent; abaxial surface with similar hairs on main veins and finer hairs on tertiary venation, these so fine that surface appears almost glabrous; petiole short relative to lamina, 0.13–0.2 × length, 1–2 cm long. Flowerclusters borne along leafless inflorescence-bearing axes, these unbranched, unisexual or bisexual, 1 per axil, up to 12 cm long, male axes ± pendulous 5–10 cm long often arising mainly from lower axils, female axes erect but pendulous near tip (1.5–)5–10(–18) cm; axes with abundant adpressed or ± spreading hairs; bracts broadly triangular, 2 by 1 mm, acute or acuminate; male clusters usually ± contiguous, 2– 3 mm diam with less than 10 flowers, female clusters densely congested into thick continuous mass along axis, each cluster 3–4 mm diam, with more than 50 densely crowded flowers (light pink in live state); bracteoles inconspicuous less than half of flower length, oblong to broadly triangular, with rounded or acute apex. Male flowers 4-merous, sessile, mature buds depressed-globose, c. 1.5 mm diam, dorsal appendage of tepals indistinct or broad flap-like, pubescence abundant, fine, adpressed. Stigma 0.5–1 mm long. Fruiting perianth narrowly ellipsoid or obovoid, very variable in length, (1–)1.5–2(–2.5) mm long, but consistently narrow, c. 0.5 mm wide, much-flattened except for central thickened part, occupying only distal third or quarter of fruiting perianth; leaf apex ± truncate, without beak or abruptly slightly constricted at apex into minute or conspicuous beak; base gradually long tapering; indumentum spreading, abundant but minute and inconspicuous.
Distribution ― Southern China (including Hong Kong and Taiwan), Japan (only Ryukyu and Bonin Islands), Philippines (Luzon).
Habitat & Ecology ― Dry broad-leaved primary forest, secondary forest; forest margins and thickets, rocky riverbanks, roadsides, cliffs often amongst Selaginella ; walls; coral limestone rock; 20–1650 m altitude.
Conservation status ― Formal assessment for each variety is considered meaningful in this case, where geographical range and identity can be established with certainty. We consider the typical variety as Near Threatened (NT). It is known from c. 150 collections but most of these are over 50 years old. Its main distribution is on Luzon in the Philippines, Taiwan and adjacent parts of south-eastern China with a few widely scattered records, one from Yunnan and a few from the Ryukyu Islands. For this reason, and because of the many old records, the EOO of 2 260 570 km 2 is misleadingly optimistic. It occurs in a range of fairly dry habitats.As discussed under B. beyeri and B. heterophylla , natural habitats in the Philippines are subject to severe and continuing degradation; there is similar, but less serious, pressure on the natural habitats in Taiwan. Although it does not meet the criteria for a formal status of Vulnerable (VU), it appears to be at risk.
For var. boninensis , we consider it meaningful to give a formal threat rating of Endangered (EN) since it is restricted to two island habitats (Bonin and Ryukyu Islands) which have suffered major habitat destruction from factors such as the introduction of goats. We base this on the criteria EN B2ab(iii).
Notes ― 1. The two regional variants of this species are here recognised as partly sympatric varieties, var. densiflora occurring from Ryukyu Islands to Taiwan, Hong Kong and Luzon, var. boninensis restricted to two island groups, Ryukyu and the Bonin Islands further west. The two varieties are usually easily distinguished, leaves in var. boninensis being relatively broad, (length 2–2.5 × width) mostly broad-acute or obtuse, in var. densiflora usually much narrower (length ≥ 4 × width), mostly narrow-acute to attenuate. However, a few collections of var. densiflora from Taiwan have leaves approaching the proportions of var. boninensis (length only 3.2–3.5 × width) and the range of variation in leaf apex partly overlaps; they are therefore recognised only at varietal rank.
2. Var. densiflora is distinguishable from other Boehmeria taxa in its leaves long, narrow, hairs fine, adpressed, marginal teeth minute but wide-spaced, sharp-acute, stipules rather short broad. Broad-leaved forms with length <5 × width are not easily confused with other taxa, but leaf proportions are rather variable and narrower-leaved forms can be confused with the partly sympatric ( China, Guangdong) B. penduliflora which is distinguished by leaves (except the youngest pair at the extreme stem apex) glabrous adaxially and spreading-hairy abaxially, with marginal teeth closer-spaced usually much more numerous, giving the margin a very different appearance clearly visible to the naked eye, also often markedly bullate and stipules longer and narrower. As discussed in detail in Note 2 under B. penduliflora, Wang (in Wang & Chen 1995) and Acharya et al. (2002) regarded B. penduliflora and B. densiflora ( var. densiflora ) as varieties of the same taxon (these authors did not refer to var. boninensis ).
3. Both varieties of B. densiflora are rather similar to the Philippine endemic B. multiflora which differs in leaves with spreading hairs both sides and mostly relatively broader, length 3(–4) rather than (3.7–)4–7 × width, inflorescence-bearing axis often much longer and stipules longer, narrower.
4. Var. densiflora is sometimes confused with B. hamiltoniana (partly sympatric but found in south-western rather than south-eastern China) which has leaves of somewhat similar shape but glabrous adaxially and always thin-textured, its inflorescence-bearing axis dichotomous at the base and a higher, only partly overlapping, altitudinal range.
5. The leaves of B. zollingeriana var. podocarpa (long, narrow, tapering, occasionally sparsely hairy) can also be confused with var. densiflora when the diagnostic axillary male clusters and long apically branched female axes are lacking; they differ in teeth usually much finer and blunt, at least one lateral vein arising somewhat lower, and petiole often longer relative to lamina.
6. Boehmeria densiflora has also been confused with some variants of the very variable and widespread B. virgata subsp. virgata var. virgata (sympatric in the Philippines). Boehmeria virgata var. virgata is easily distinguishable in flower and fruit from both varieties of B. densiflora , having inflorescence-bearing axes ± pendulous, slender with well-spaced clusters, the females long (20–70 cm) and sometimes branched, male axes also often> 15 cm long, usually branched throughout length, but it is almost identical to B. densiflora in stipules and range of leaf texture and is rather variable vegetatively.
Table 2 gives the characters for distinguishing sterile material of B. virgata var. virgata from B. densiflora . It is distinguishable from both varieties by its indumentum, and additionally from var. densiflora on leaf proportions, sometimes also on marginal tooth shape and proportions, and from var. boninensis additionally on shape and/or dimorphism of apex of larger and smaller leaves.
Key to varieties
1. Leaf length (3.2–)4–7 × width. — China (incl. Taiwan); Japan (Ryukyu Islands); Philippines (Luzon)... a. var. densiflora View in CoL
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