Boehmeria grandis (Hook. & Arn.) A.Heller

Wilmot-Dear, C. M. & Friis, I., 2013, The Old World species of Boehmeria (Urticaceae, tribus Boehmerieae). A taxonomic revision, Blumea 58 (2), pp. 85-216 : 141-143

20. Boehmeria grandis (Hook. & Arn.) A.Heller — Fig. 18 ; Map 20

Boehmeria grandis (Hook. & Arn.) A. Heller (1897) 812. ― Urtica grandis Hook. & Arn. (1837) 95. ― Type: Beechey s.n. (holo BM; iso K), Hawaiian Islands, Oahu.

Boehmeria stipularis Wedd. (1854) 200. ― Syntypes: du Petit­Thouars s.n. (not traced), Mascarene Islands ; Gaudichaud s.n. (not traced), Reunion; Commerson (P), Mauritius.

Boehmeria amplissima Blume (1857) 219 ― Type: Richard 690 (iso P), Réunion.

Boehmeria grandis (Hook. & Arn.) A.Heller var. kauaiensis Skottsb. (1926) 220. ― Type: Skottsberg 951 (holo GB, n.v.), Hawaiian Islands, Kauai , Waimea .

Boehmeria grandis (Hook. & Arn.) A.Heller var. cuneata Skottsb. (1944) 350. ― Type: Cranwell 3392 (holo GB), Hawaiian Islands, Molokai , 20 Sept.1938.

Shrub, to 7 m tall; ultimate stems relatively robust, (1.5–) 2.5–3 mm diam, hairs sparse or abundant, adpressed or spreading, ≤ 0.4(–0.5) mm long. Stipules connate to apex, large, boat-shaped, (10–)25–65 by (3–) 7–20 mm, pubescent outside in a broad band and with prominent parallel venation, very soon deciduous. Leaves opposite, not or slightly dimorphic in size and shape (‘smaller’ leaves slightly relatively broader), elliptic or elliptic-ovate, often very large and broad, (9–)12–21 by (4–) 7–12.5 cm, length (1.2–)1.5–2(–3) × width; margin up-curved-serrate, teeth (20–)25–50 either side, medium or large, well-spaced, 1–2 by 2–6 mm; leaf apex short broad attenuate-acuminate; base narrowly rounded or slightly cordate (in the Mascarenes distinctly cordate, with auricles overlapping or wrapped around the petiole); basal veins extending into distal third of lamina, upper lateral veins numerous (5–)6–9, subopposite, all arising in distal half of lamina but often hard to distinguish from robust coarser tertiary veins in proximal half, veins visible or somewhat impressed adaxially and finely prominent abaxially, coarser tertiary veins scalariform, conspicuous or sometimes inconspicuous; texture chartaceous, leaves thin or thick and bullate; adaxial surface glabrous or with sparse adpressed hairs except on veins; hairs on abaxial surface usually on veins only, sparse, adpressed or abundant, longer, spreading; petiole relatively long, 0.3–0.5(–0.8) × lamina length. Flower­clusters borne on ± erect leafless inflorescence-bearing axes, these arising one from each axil, mostly unisexual, branched throughout length; male axes 20–30 cm long with robust main axis and long lateral branches with 2nd-order branching, female more slender, 7–13 cm with lateral branches shorter and unbranched; bracts triangular, 2 by 1 mm; male clusters spaced 2 –10 mm, tiny with 1–few flowers, female clusters generally more crowded, spaced 1–3 mm, clusters 1.5–2 mm diam, with few–20(–more than 40) fairly crowded flowers; bracteoles obovoid or oblong-spathulate, 0.3–0.5 mm long, only conspicuous once flowers have fallen. Male flowers 4-merous, sessile, mature buds depressed-globose, 1.2–1.4 mm, segments divided almost to base, dorsal appendage of tepals thick, prominent, hairs abundant, fine, spreading. Female flowers broadly ovoid, flattened, 0.5 by 0.3 mm with abundant coarse hairs; stigma 1–1.5 mm long. Fruiting perianth 1–1.2 by 0.5–1 mm, ovoid or with rhombic outline, markedly laterally flattened into narrow or wide wings up to 0.3 × total fruiting perianth width. Achene elongate and occupying middle third of fruiting perianth.

Distribution ― Hawaiian Islands (incl. Hawaii, Mauai, Lauai, Molokai, Oahu, Kauai); presumed naturalised in Reunion and Mauritius.

Habitat & Ecology ― Ravines and clearings in rainforest, exposed slopes and ridges, often forming dense thickets; 130– 1100 m altitude.

Conservation status ― Vulnerable (VU). The species is known from c. 300 collections, although most of them are more than 50 years old. There is habitat destruction on all the Hawaiian Islands, but also conservation efforts and the existence of forest reserves where many of the collections come from. The EOO in its presumed native distribution is 16 760 km 2, which meets the criteria for Vulnerable, as does the AOO of less than 500 km 2. This would justify the conservation status VU 2Bab(iii). However, if one includes the records from the Mascarene Islands where the habitat destruction is as severe as in the Hawaiian Islands, the EOO becomes meaninglessly large, and criteria based on EOO can no longer be used. But the AOO remains less than 500 km 2, and would still justify a status of Vulnerable. However, with two far removed populations it seems unlikely that the species would become extinct.

Notes ― 1. This is the only species of Boehmeria known from Hawaii. It is distinctive in stipules extremely large, connate and boat-shaped, (10–) 20–60 mm long, and leaves large, only sparsely hairy, relatively broad, often bullate and ridged, drying brownish, with many upper veins and almost equally robust tertiary veins spaced throughout lamina. Its strongly-veined leaves and branched female inflorescence-bearing axes are reminiscent of those of the Himalayan B. polystachya .

2. Marginal teeth in B. grandis are very varied in number and width relative to leaf-size and some forms can be confused with some Southeast Polynesian forms of the very variable B. virgata var. virgata which also have large thick leaves and stipules unusually large for B. virgata . However, B. virgata differs in male axis without 2nd-order branching, female axes unbranched or with short male branches at base; larger-toothed forms often also have margin crenate (teeth rounded) rather than serrate, leaf texture smooth rather than bullate and secondary veins distinct from tertiary. Some collections of B. virgata appear somewhat intermediate with B. grandis (discussed in Note 5 under B. virgata var. virgata ).

3. Forms with the smallest stipules are rather similar to the largest forms of B. rugosissima (Jawa, Philippines) which differs in lateral veins fewer but more distinct all clearly arising in distal half, and fruiting perianth less markedly flattened with indistinct wing and relatively large achenes.

4. The material found in Mascarenes ( B. stipularis ) is indistinguishable from that found in Hawaii. The differences suggested in literature (e.g., Hillebrand 1888: 412) between these two taxa are non-existent; B. stipularis appears to differ from B. grandis only in leaves strongly cordate, often with marked auricles overlapping each other or wrapped round the petiole, lamina often abundantly velvety hairy abaxially, stigma 1.5 mm. Wagner et al. (1999: 1300) note that Heller (1897) recognised the Hawaiian taxon as distinct “without any comment other than, when considered conspecific with B. stipularis , it had an odd distribution”. It is presumed to be an early introduction to the Mascarenes from Hawaii (just as is the presence there of the East Asian B. penduliflora ). The species was cultivated by the early Hawaiians for fibre ( Degener 1947: Fam. 97, Urticaceae , Boehmeria ).

5. There is some regional variation within the Hawaiian Islands which appears to be genetic rather than environmentallyinduced. Throughout the Hawaiian Islands occur typical forms with stems robust, stipules very large, leaves broad, prominently reticulate-veined and often very large, but a variant which has been recognised as var. kauaiensis occurs only in Kauai, with ultimate stems slender, c. 1.5 mm diam (rather than c. 3 mm), stipules only 10–35 (rather than 25–65) mm, leaves only up to 12 cm long, length 2 –3 × (rather than 1.2–2.2 ×) width, margins with only up to c. 30 teeth, veins less prominent and tertiary reticulation inconspicuous. The two forms are fairly distinct in Kauai but elsewhere (especially in Molokai) the distinction completely breaks down and it is therefore not formally recognised here.

6. Two forms occur on Reunion (Boyer, pers. comm.) almost identical in leaves and flowers but very different in habit. A large shrub, 2–4 m tall, is widespread on the island, with many weak arching branches which send up vertical leafy shoots to 7–10 m, with fibrous aerial roots at shoot junctions, stipules persistent and flowering once a year. However, in only one locality the species occurs as trees up to 8 m, 13– 20 cm diam, with a single unbranched trunk or with one or two strong branches in upper half of plant, without arching branches or aerial roots, stipules deciduous even from near stem apex, flowering twice a year, in July and October. Boyer has suggested that this variation is a result of environmental damage from which the widespread form is regenerating whereas the very localised tree form grows in a locality which has somehow escaped damage.

Figures

Map 20 Distribution Boehmeria grandis (Hook.& Arn.) A.Heller;indigenous on the Hawaiian Islands (above) and naturalised distribution on the Mas- carenes (below).

Fig. 18 Boehmeria grandis (Hook. & Arn.) A.A.Heller. a. Habit of stem with inflorescence-bearing axes; b. detail of one node with branched inflorescencebearing axes; c. leaf; d. detail of stem apex with leaf and stipule; e. detail of male inflorescence-bearing axis with branch, flower-clusters (inflorescences) and bracts; f. male bud; g. detail of female inflorescence-bearing axis with flower-clusters (inflorescences) and bracts; h. fruiting perianth (a: Selling 3098; b, e, f: Cowan 679; c: Boyer 3; d: Christofferson 3702; g: Degener 8696; h: Bosser 20880; all K). — Scale bars: a, c, d = 2 cm; b = 1 cm; e, g = 2 mm; f, h = 1 mm.