Hyptidendron albidum Harley & Antar, 2017

Harley, Raymond Mervyn & Antar, Guilherme Medeiros, 2017, Hyptidendron albidum (Lamiaceae, Hyptidinae), a remarkable new species from northern Minas Gerais state, Brazil, Phytotaxa 308 (1), pp. 97-103 : 98-102

Hyptidendron albidum Harley & Antar sp. nov. ( Figs. 1 − 2 )

The new species shares with Hyptidendron unilaterale a similar unilateral cymose inflorescence structure, differing from it in the indumentum composed of white dendroid trichomes, the shorter inflorescence obscured by the leaves and the leaf base frequently cordate.

Type:— BRAZIL. Minas Gerais: Itacambira, estrada Juramento—Itacambira, cerca de 20 km de Juramento, cerrado pedregoso, 17 December 2003, fl., fr., Souza et al. 29588 (holotype SPF!, isotypes ESA!, HUEFS!, K!, RB!).

Erect shrub or subshrub, 1 − 1.5 m tall, all vegetative parts densely covered with white, dendroid trichomes, densely branched; stems woody, at least in upper part, <4 − 5 mm in diameter, ± rounded in cross-section. Cauline leaves opposite, ascending, longer than internodes, imbricate, diminishing in size towards stem apex, lamina 2.2 − 3.4 × (1.4 −) 1.9 − 3.2 cm, coriaceous, whitish, the older ones brown and less hairy, rounded to broadly ovate, or rarely ovateoblong, base cordate, rarely truncate or rounded, apex obtuse to acute, usually very shortly apiculate, margin sharply serrate, with (8 −)13 − 26 teeth on each side of leaf, the tooth apex swollen and sub-glabrous (hydathodes not confirmed, but most probably present), adaxial surface with venation scarcely impressed, abaxial surface with venation reticulate, midrib and primary veins slightly prominent, but obscured by indumentum, which is denser on abaxial surface, and with scattered sessile glands; petiole 1 − 6 mm long. Inflorescence a terminal thyrse of shortly pedunculate cymes subtended by foliaceous bracts, which are conspicuous, similar to the leaves, but smaller, sub-imbricate, and shorter than the cymes, mature cymes 10 − 20 flowered, mostly unilateral and borne on peduncles 6 − 10 mm long. Flowers on pedicels 1 − 3 mm long and subtended by narrowly linear, almost subulate bracteoles 1 − 2 mm long; calyx at anthesis 5 − 5.5 mm long, tube 3 − 3.8 mm long, straight, slightly turbinate, externally densely white-tomentose, the branches of the trichomes sometimes terminating in a pale yellow, spherical gland, tube internally glabrous (especially frequent on the calyx lobes), calyx lobes subequal, 1.8 − 2.2 mm long, deltate, densely white-tomentose externally and internally more sparsely hairy, calyx in fruit 7.5 − 8.5 mm long, with tube accrescent in fruit, 5.8 − 6.7 mm long, ± cylindrical; corolla purplish or lilac, 6 − 7 mm long, tube 3.5 − 4 mm long, straight, narrowly cylindrical, 0.7 − 0.9 mm wide, externally rather densely, but unevenly white-tomentose, glabrous within, lobes spreading, the anterior lobe large, boat-shaped with long, almost caudate apex; anterior stamens with glabrous to glabrescent filaments, posterior pair with filaments hairy, gynoecium with style jointed and well-developed stylopodium protruding above ovary, and apically with two slender stigmatic lobes. Mericarps 3.0 − 3.5 × 1.5 − 1.8 mm, oblong-ellipsoid, dark castaneous, rugulose and shining, glabrous, with deep abscission scars, not mucilaginous when wetted.

Distribution, habitat and phenology: — Hyptidendron albidum is known from only four localities in three municipalities in Northern Minas Gerais, SE Brazil ( Fig. 2 ). It can be found up to 1000 m elevation in highland rocky fields (Campo rupestre), rocky savannah or savannah physiognomies, all of these included in the Cerrado domain. Hyptidendron albidum has been found in a fertile condition from September to March.

Conservation Status: —The area of occupancy is very reduced, being just 24,000 km ². It is known only from six collections, none of those located inside protected areas. With the rapid advance of Cerrado deforestation, mostly for pasture or crops, the Cerrado flora, throughout the domain is largely threatened. It is estimated that more than 50% of its original area has already been replaced ( Beuchle et al. 2015). Within the area where Hyptidendron albidum occurs much agricultural activity, involving habitat destruction, has been noted. Also, some populations are very close to the highway. The conservation status of this species is assessed as Endangered according to criteria B1ab(iii)+2ab(iii) ( IUCN 2001).

Etymology: —The specific epithet refers to the indumentum of all vegetative parts, which are densely covered with white, dendroid trichomes.

Additional specimens (paratypes):— BRAZIL. Minas Gerais: Grão Mogol, MG-15, Fazenda Tamanduá , 10 September 2005, fl., Tameirão-Neto 4020 (BHCB!, HUEFS!) ; Itacambira , 17º00.572’’S, 43º20.266’’W, 1300 m, 13 November 2001, fl., fr., Tozzi & Alencar 2001-474 ( UEC!) ; ibid., estrada Itacambira—Juramento, 9 km de Itacambira , 16º58’ 58.07’’S, 43º32’04.6’’W, 1100 m, 23 February 2002, fl., fr., Souza et al. 28223 (ESA!, HUEFS!, SPF!) ; Juramento, rodovia Montes Claros a Itacambira , Serra do Catuni , 17 March 1997, fl., fr., Hatschbach et al. 66389, (K!, MBM!) ; ibid., Serra do Catuni , 1000 m, 4 December 2004, fl., fr., Hatschbach & Barbosa 78829 (K!, MBM!) .

Affinities and morphological notes:— Hyptidendron albidum can be immediately recognized from all other species of the genus on account of its dense indumentum of white dendroid trichomes covering much of the plant, allied with its inflorescence composed of a unilateral cymose structure.

The species which shows greatest morphological similarity is Hyptidendron unilaterale ( Epling 1951: 140) Harley (1988: 93) , which displays a similar unilateral cymose structure. It can be distinguished from Hyptidendron albidum by the following characters: the latter species having an indumentum composed of white dendroid trichomes (vs. indumentum of dense, short, glandular trichomes with scattered long uniseriate trichomes), leaves with cordate, or rarely truncate or rounded base (vs. leaves with a rounded base), mature inflorescences obscured by the leaves, hardly surpassing leaf size, up to 3.0 cm long (vs. mature inflorescences not obscured by leaves, surpassing leaf size, up to 6 cm long), pedicels 1 − 3 mm long (vs. pedicels 1 − 5 mm long) and calyx tooth at anthesis 1.8 − 2.2 mm long (vs. calyx tooth at anthesis 1 − 1.5 mm long).

Hyptidendron albidum is also similar to other species of the former Hyptidendron sect. Umbellaria , in which it seems to belong. The main morphological differences among H. albidum and related species are summarized in Table 1. It is also superficially similar to two species of the former Hyptidendron sect. Hyptidendron : Hyptidendron canum (Pohl ex Bentham 1833: 135) Harley (1988: 90) and H. leucophyllum (Pohl ex Bentham 1833: 134) as those species share a similar indumentum of white dendroid trichomes. Still, H. canum and H. leucophyllum have flowers arranged in terminal cymose panicles and Hyptidendron albidum has flowers arranged in unilateral cymes.

In several species previously placed in Hyptidendron sect. Umbellaria the cyme structure is mixed. Often the branches from the lowest nodes of the cyme may be dichasial, while distally these become unilateral, with the branching taking a scorpioid appearance. The complexity of the cyme structure within this group caused Epling to make some conflicting statements. He suggested in the revision of Hyptis ( Epling 1949) that Hyptis unilateralis Epling (1951: 140) is the only species of Hyptis sect. Umbellaria with a unilateral cymose inflorescence, using it to separate this species in the key from all other members of the section. However when validating the publication of Hyptis unilateralis he compares it to Hyptis glutinosa Bentham (1848: 130) , on the grounds that both show a similar cymose structure ( Epling 1951). We believe that further studies of inflorescence structure are required to clarify the differences and relationships between the species of this group, which presents great taxonomic complexity and species without taxonomic resolution.

Figures

FIGURE 1. Hyptidendron albidum. A. Branch bearing leaves and inflorescenses. B−C. Leaves, adaxial surface with indumentum detail. D−E. Leaves, abaxial surface with indumentum detail. F. Immature cyme. G. Flower, side view. H. Calyx with bracteole, side view. I. Corolla, side view. J. Gynoecium and style, showing stylopodium. K. Mericarp. A−K. Illustration of Laura Montserrat based on Souza et al. 29588 (SPF).

FIGURE 2. Hyptidendron albidum. Holotype at SPF.