Hydnora arabica Bolin & Musselman, 2018

Bolin, Jay F., Lupton, Darach & Musselman, Lytton John, 2018, Hydnora arabica (Aristolochiaceae), a new species from the Arabian Peninsula and a key to Hydnora, Phytotaxa 338 (1), pp. 99-108 : 100-103

Hydnora arabica Bolin & Musselman , sp. nov. ( Figs. 1–4 )

Diagnosis: — Hydnora arabica is similar to Hydnora abyssinica , but can be distinguished by having red to orange inner perianth tube color and tepal lobe margins entirely covered with dense strigose setae.

Type: — SULTANATE OF OMAN. Dhofar region: Ayn Ayuoon. 0.66 km SE of the spring. Flowers emerging from deep alluvial sand, on margin of main wadi bed, parasitizing Acacia tortilis , other dominant vegetation Salvadora persica, Lycium shawii, and Ziziphus spina-christi , 660 m, 17°14’28.66”N, 53°53’29.92”E, 16 December 2014 J. Bolin, S. Al Rahbi, L. Musselman JFB2014 OM 3 (holotype OBG!, isotype US!).

Herbaceous perennial root holoparasite. Rhizome terete, subterete, or compressed (1–5 cm wide, may be much larger on mature specimens, but not seen), rhizome surface coriaceous, dark brown to light tan, lighter colored (when fresh) near growth tip, rhizome spreads laterally and may bifurcate or branch irregularly, rhizome ornamented with numerous lateral tuberculate appendages that can form haustoria , branches of the rhizome, or flower buds, numerous flowers and flower buds on single rhizomes, rhizome swollen and irregular at haustorial interface with host root and rhizome fleshy, pink to red internal tissue when broken, lighter colors at growing tip (in life). Merosity usually 4, though 3 and 5 observed. Flower emerges only partially from soil. External perianth tissues brown to reddish brown and scaly (in life), perianth tissues fleshy, internal perianth tube and tepal lobe tissues red to orange (in life), darkening to brick red-brown, perianth tubular 10–28 cm long (total length) × 1.9–3.6 cm wide (tubular portion), tepal lobe length measured from apex to point of connation with adjacent tepal 4.0– 8.5 cm, tepal lobe width measured at midpoint 1.9– 3.5 cm (on 4–merous flowers, wider on 3–merous and narrower on 5–merous flowers), tepal lobes clavate to elongatelinear and typically curved, not fused at apex, and dense strigose setae on margins of tepal lobes (max. 3.3 mm) covering entire tepal lobe margin from ventral to dorsal edge. Two floral chambers, an androecial chamber subtended by a gynoecial chamber, inner surfaces of chambers glabrous, perianth chambers joined by antheral ring with a central orifice, formed by connate anther lobes. Osmophores oriented on the ventral surface of the tepal apices, osmophore spongy and white (in life) generating fetid odor, and osmophore darkens to tan when dried. Ovary inferior unilocular with numerous ovules, ovary 25–45 mm wide, lobed and cushion-like stigma on the floor of the gynoecial chamber, and stigma width 19–22 mm. Only one fruit observed, globose, (7 cm in diameter). Subterranean fruit contained thousands of spherical black-brown seeds, diameter 0.7–1.2 mm. Parasitic on the roots of Acacia tortilis Forssk. (1775: 150) Hayne (1825: 10 : pl. 31) and Pithocellobium dulce Bentham (1844: 199) Roxburgh (1798: 67) .

Distribution: —Known from southern Oman (Dhofar region) and Yemen. Collected from an elevation of 200 to 680 m ( Fig. 1 ).

Habitat and Ecology: — Hydnora arabica is an obligate root parasite of Fabaceae that is visible above the soil surface only when flowering ( Fig. 2 ). Most of our collections in Oman occurred on Acacia tortilis and the same host was reported from Yemen ( Al-Fatimi 2015). Interestingly, in a small Dhofar settlement approximately 16 km NE of Mirbat, adjacent to Ayn Ayuoon south of Jebel Samhan, we were directed to a robust H. arabica population associated with and below the non-native Pithocellobium dulce (5 m high) in the settlement courtyard and goat yard. No other potential host trees were within 50 meters, thus P. dulce was likely the host plant. The villagers mentioned that the goats fed in the nearby wadi where H. arabica was abundant and were the likely vector of Hydnora seeds into the settlement. Interestingly, in Madagascar, the same introduced host P. dulce was a common host of H. esculenta ( Bolin and Musselman 2013) .

The apparent primary host Acacia tortilis is abundant in northern Oman and present across much of the Middle East; however, the parasite H. arabica is apparently restricted to the southern portion of the Arabian Peninsula. In Oman, the gravel plains separate the Northern and Southern mountains ( Patzelt, 2015) and are a phyotogeographic barrier to dispersal. The plains are hyper-arid without natural springs, or temporary or permanent water bodies. Rainfall is sporadic from year to year, often with several years between rainfall resulting in a sparsely vegetated landscape with low levels of species diversity ( Ghazanfar, 2004). The general geology and soils of the type locality, Ayn Ayuoon, were mountainous with strongly dissected rocky plateaus and loamy-skeletal to sandy-skeletal shallow soils underlain by formations of the Tertiary, Hadhramaut group - beige bioclastic, calcarenitic and micritc limestone with abundant fossilized mollusks ( Platel et al. 1992).

We observed H. arabica in southern Oman flowering in December but local villagers reported that flowering also occurs in other months. At some sites flowering was reported in July and at others in May; the apparent sporadic flowering may be dependent on adequate rainfall. Fruits of other Hyndora species are slow developing, only maturing 2–4 months after anthesis ( Bolin et al. 2009).

Etymology: —The specific epithet refers to the distribution of H. arabica on the Arabian Peninsula.

Vernacular Name: —Thesiger reported the vernacular name as dhanuna on herbarium material from the 1940s. Miller and Morris (1998) give the Jibbali name xamleg and the Dhofari Arabic names khamlayyeh and khumla’ah. We can confirm that Jibbali settlers in Dhofar that knew the plant well as a potential food item in fruit used the name xamleg. From Yemen in the districts of Lawdar and Dathina that use the plant the Arabic local names of nabeekh, fateekh, and tarateef ( Al-Fatimi et al. 2015) are used.

Conservation Status: —In the Dhofar region of Oman, dried rhizomes of H. arabica were common in most wadi beds with an abundance of its common host Acacia tortilis , though fresh flowering material was difficult to locate due to its infrequent flowering and primarily hypogeous habit. Based on our observations, the conservation status of H. arabica in southern Oman is secure. However, H. abyssinica is reported as rare in Saudi Arabia ( Collenette 1999) and we have little basis to comment on H. arabica abundance in Yemen.

Additional specimens examined: Hydnora arabica sp. nov. OMAN. Dhofar region: SE of the Empty Quarter Dhofar: (Rub el-Khali) near Wadi Haluf , 8 November 1945, W. Thesiger s.n. ( BM) ; Oman Um Shedid , 31 October 1946, W. Thesiger s.n. ( BM) ; Mughsin El Ain, no date, W. Thesiger s.n. ( BM), Wadi Masila , 14 April 1947, W. Thesiger s.n. ( BM) ; Zufar, 50km west of Mudhai , 13 September 1985, A. Miller 7619 ( RGBE, ODU) ; Approx 17 km NE of Mirbat, Wadi Ayn south of Jebel Samhan , 310 m, 17° 7’2.64”N 54°47’53.21”E, 15 December 2014, J. Bolin, D. Lupton, L. Musselman, S. Al Rahbi JFB2014 OM1 ( OBG) ; Approximately 2 km south of the village of Haluf, Wadi Haluf , 680 m, 17°20’3.56”N 53°57’35.82”E, 16 December 2014. J. Bolin, S. Al Rahbi, L. Musselman JFB2014 OM2 ( OBG) ; Approximately 16 km NE of Mirbat. In small settlement adjacent to Wadi Ayn south of Jebel Samhan , 200m, 17° 5’40.62”N 54°48’35.53”E, 17 December 2014, J. Bolin, S. Al Rahbi, A. Rahman, L. Musselman JFB2014 OM4 ( OBG) .

Figures

FIGURE 1: Distribution of Hydnora arabica and Hydnora abyssinica in the Arabian Peninsula.A single collection of Hydnora abyssinica (Collenette 5119, K, RGBE), represented by a black circle (•) is reported from southwestern Saudi Arabia, approximate location. For Hydnora arabica open circles (O) are approximate locations from the literature and from herbarium labels without precise locality information. Black triangles (▲) represent collections conducted by the authors during Dec. 2014 based on GPS coordinate information. The recent Hydnora arabica collections with color photographs have been reported from Abaya Province, Yemen, grey shaded area (Al- Fatimi et al. 2015).

FIGURE 2.A) Hydnora arabica flower emerging from soil. White osmophores apparent on tepal apices; B) Excavated mature H. arabica flower, flower bud, and growth tip of rhizome; C) Cross section of terete rhizomes and growth tip of rhizome covered in numerous tubercle-like lateral appendages (Fig 1A–1C: J. Bolin, S. Al Rahbi, L. Musselman, JFB2014OM3); D) Dried berry and flower from previous season, numerous dark spherical seeds inside broken fruit (from J. Bolin, D. Lupton, L. Musselman, S. Al Rahbi, JFB2014OM1). Scale bars A) = 1 cm; B) 4 cm; C) 2 cm; D) 1 cm.

FIGURE 3: A) Photo of a H. abyssinica fresh open flower and open buds showing habit and bright red internal perianth coloration (Bar=4.0 cm) B) Close-up of apical osmophore (white) and dense strigose tepal margin setae. (Bar=0.5cm) both photographs taken by Anthony Miller, Sept. 1985 (Miller 7619, RBGE, ODU).

FIGURE 4. Comparison of tepal margin setae of H. arabica and H. abyssinica. A) Dense strigose tepal margin setae from H. arabica (J. Bolin, S. Al Rahbi, L. Musselman, JFB2014OM3); the next panels show H. abyssinica with some variation in the tepal margin setae considered diffuse with with remote apices, B) H. abyssinica (BolinJB_09_8, WIND) C) H. abyssinica. (Musselman 6279a, US D) H. abyssinica (Luke 7182, US). (Size Bars = 1 mm)