Argemone × hybrida R.Otto & Verloove

Otto, Rainer & Verloove, Filip, 2016, A new natural hybrid in Argemone (Papaveraceae), Phytotaxa 255 (1), pp. 57-65 : 58-62

Argemone × hybrida R.Otto & Verloove , hybr. nov. ( Figs. 1–5 )

( A. mexicana L. × A. ochroleuca Sweet )

Diagnosis:—Intermediate in morphology between Argemone mexicana and A. ochroleuca , but usually more vigorous. It differs from both parents by the slightly larger petals, 35–45 × (25–)30–35(–40) mm which are paler than in the former but darker than in the latter (lemon to light yellow); the larger flower buds, 13–19(–22) × 8–12 mm; the smaller capsules, 15–23 × 7–10 mm; and its complete sterility. The pollen mass of the hybrids contains “minigrains” (13–19 μm) unlike the pollen of both parents.

Type:— SPAIN. Canary Islands: La Palma, Sta. Cruz de La Palma, Barranco de las Nieves parallel to Avenida de las Nieves, dry gravelly exposed riverbed, in open ruderal vegetation, several specimens among A. mexicana and A. ochroleuca , 41 m, 28.68926º N, 17.765060º W, 4 August 2014, R. Otto 21182 (holotype: BR!; isotype: priv. herb. R. Otto!).

Description:—Plants annual (?) or more often short-lived perennial, with latex bright yellow; flowering abundantly all year round. Stems glaucous, leafy, sparingly prickly, moderately to richly branched from base and distally, 50–100 cm tall, lower branches often very long and spreading, vigorous specimens well over 100 cm wide and tall, squarrose with decumbent basal branches and basal stem diameter up to 20 mm or more, older plants produce new branches basally. Leaf blades bluish-green, conspicuously white-bluish mottled over veins, adaxially nearly unarmed, abaxially sparsely prickly on the veins, pinnately divided to more than halfway, lobes broadly dentate, the tooth ending in strong spines, the middle and upper leaves usually clearly clasping the stem. Inflorescences: buds oblong, ca.1.5 times longer than wide, 13–19(–22) × 8–12 mm; sepals 3, obovate, 3–7 prickles per sepal, horns terete, unarmed, up to 14 mm long (including apical spine); flowers (6–)7–8(–9) cm wide, subtended by (1–)2(–3) foliaceous bracts; petals 6, lemon to light yellow, obovate, up to 3.5–4.5 cm long and (2.5–)3–3.5(–4) cm wide; stamens 40–70, filaments yellow, up to 11 mm long; anthers bright yellow, oblong, open, 1.5–2.5 mm long, curved after flowering; pollen contains ca. 7% of “minigrains”, 13–19 μm in diameter; pistil 4–6-carpellate; ovary ovate, 9–11× 5–6 mm, covered with adpressed and pointed stramineous spines with darker base, to 6 mm long; stigma purple-red to purple-brownish, 3–5 mm wide, 1.5–2.5 mm high, dissected, lobes moderately to strongly spreading, the pale bluish non-receptive area of the stigma visible. Capsules erect, oblong, 15–23 × 7–10 mm (incl. stigma and excl. prickles), slightly grooved on sutures, dehiscing on top or indehiscent, with numerous striking stramineous prickles with expanded glaucous base, these adpressed or erect-patent, variable in size, longest prickles 5–10 mm long, style and stigma persistent, only aborted seeds present.

Argemone × hybrida is intermediate between its parents in nearly all vegetative and floral characters. The most important diagnostic features among Argemone mexicana , A. ochroleuca and A. × hybrida are summarized in Table 1 and illustrated in Fig. 4 .

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The presence of “minigrains” is (beside other pollen anomalies) a particularly characteristic feature of the hybrid, since these are always absent in A. mexicana and A. ochroleuca (see Chaturvedi et al. 1999). These “minigrains” have the appearance of normally developed pollen grains, but they are less than half the length of the normal grains. According to our own counts “minigrains” represent ca. 7% of the pollen mass.

Distribution:—Potentially naturally occurring in parts of Mexico where both parents grow sympatrically (e.g. in the states Guerrero, San Luis Potosí, Tamaulipas and Vera Cruz; Ownbey 1958). Since both species have widely been introduced in temperate and (sub-) tropical areas worldwide, their hybrid potentially is relatively widespread but overlooked. However, natural hybrids seem to have been rarely reported and are even absent from the native area. To our knowledge they have only been reported so far from the Indian subcontinent (e.g. Malhotra 1960, Chaturvedi et al. 1999) and Mozambique ( Viveiros & Pereira 1970).

In the Canary Islands both Argemone mexicana and A. ochroleuca are considered invasive species ( Acebes Ginovés et al. 2009). Both compete with and possibly displace indigenous pioneer species, thus threatening biodiversity, especially in riparian habitats (see also Van der Westhuizen & Mpedi 2011). Although occupying the same type of habitats and often growing in close proximity, natural hybrids had not yet been reported so far from Europe and Macaronesia.

Notes:— Argemone × hybrida was found in two locations in the municipality of Sta. Cruz de La Palma on the island of La Palma (Canary Islands, Spain). Both places are relatively near to one another (approximately one kilometer apart at flight distance) but geographically completely separated by mountain, ravine and urban areas. In 2014 several individuals were found that clearly showed an intermediate morphology, compared with both putative parents that were found in the same localities. The most striking features of these hybrids were the intermediate petal color (light yellow) and the smaller, empty capsules (complete sterility). In addition, these plants were often noticeable bigger than either parent, more richly and profusely branched and more abundantly flowering (doubtlessly as a result of hybrid vigor).

In the first locality, about 45 individuals were found along a stretch of ca. 1.2 km in the exposed river bed of the Barranco de las Nieves, just before the river mouth. The riverbed is dry for most of the year. Water runs through the barranco very irregularly after heavy precipitation but then sometimes very strongly so. The stretch that runs through the town is mostly bordered by concrete sidewalls with access ramps in its lower part. The substrate in the barranco is sandy and gravelly. Parts of the area are sometimes transformed into a large unsurfaced parking place, after removal of all aboveground vegetation, scree and scrap, levelling the terrain. Thus, the area is frequently disturbed, permanently creating an open, sun-exposed area suitable for the establishment of thermophilous vegetation. The Argemone taxa are associated with native species like Bosea yervamora L., Hyparrhenia sinaica (Delile) Llauradó ex G.López , Kleinia neriifolia Haw. , Lavandula canariensis Mill. , Rumex lunaria L., etc. Many of the other accompanying species are of Mediterranean origin and/or cosmopolitan or pantropical weeds such as Ageratina adenophora (Spreng.) R.M.King & H.Rob. , Amaranthus hybridus L. s.str., Amaranthus viridis L., Avena barbata Pott ex Link , Bidens pilosa L., Chenopodium album L., Chenopodium murale L., Datura stramonium L., Glaucium flavum Crantz , Erigeron bonariensis L., Erigeron sumatrensis Retz. , Hirschfeldia incana (L.) Lagr.-Foss., Solanum nigrum L. subsp. nigrum , etc. The locality is also invaded by exotic species, mainly escapes from cultivation, e.g. Abutilon grandifolium (Willd.) Sw. , Datura innoxia Mill. , Dysphania anthelmintica (L.) Mosyakin & Clemants, Leonotis nepetifolia (L.) R.Br., Lycopersicon esculentum Mill. , Malvastrum coromandelianum (L.) Garcke subsp. coromandelianum , Nicotiana glauca Graham , Pennisetum setaceum (Forssk.) Chiov. , Ricinus communis L., Sida rhombifolia L. var. canariensis (Willd.) Griseb. , Tagetes minuta L. and Waltheria indica L. Erodium neuradifolium Delile ex Godr. is an accompanying species of Saharan-Arabian distribution.

In the second location three hybrid individuals were detected among the parent species. They were found on a narrow, disturbed urban slope between Carretera del Galión and Calle Teneguía, on bare ground (maybe a former lawn) and sun-exposed. Common companion plants were, among others, Amaranthus hybridus L. s.str., Amaranthus viridis L., Chenopodium murale L., Hirschfeldia incana (L.) Lagr.-Foss. and very numerous Portulaca granulatostellulata (Poelln.) Ricceri & Arrigoni.

Additional specimens examined (paratypes):— SPAIN. Canary Islands: La Palma, Sta. Cruz de La Palma, Barranco de las Nieves parallel to Avenida de las Nieves, dry gravelly exposed riverbed, in open ruderal vegetation, few specimens with A. mexicana and A. ochroleuca , 41 m, 28.68926º N, 17.765060º W, 4 August 2014, R. Otto 21180 (priv. herb. R. Otto); ibid., 09 August 2014, R. Otto 21223 (priv. herb. R. Otto, dupl. BR!); ibid., 31 October 2014, R. Otto 21365 (priv. herb. R. Otto!); ibid., Barranco de las Nieves parallel to Calle Leocrizia Pestana, dry gravelly exposed riverbed, in open ruderal vegetation, several individuals, with A. mexicana and A. ochroleuca , 85 m, 28.689966º N, 17.770343º W, 14 August 2014, R. Otto 21261 & 21262 (priv. herb. R. Otto, dupl. BR!); ibid., disturbed slope between Carretera del Galión and Calle Teneguía, open earthy ground (former lawn?), 3 specimens among the parent species, 53 m, 28.6807º N, 17.76994º W, 16 August 2014, R. Otto 21271 (priv. herb. R. Otto, dupl. BR!).

Figures

FIGURE 1. Argemone × hybrida, Sta. Cruz de La Palma, August 2014 (Photograph: R. Otto).

FIGURE 2. Argemone × hybrida (holotype), Sta. Cruz de La Palma, part of flowering and fruiting shoot (big picture), two buds and young fruit (small picture), priv. herb. RO 21182, August 2014 (Photograph: R. Otto).

FIGURE 3. Argemone × hybrida, Sta. Cruz de La Palma, flowering plant (left), flower bud (top right) and fruit (bottom right), August 2014 (Photograph: R. Otto).

FIGURE 4. Important differentiating features between Argemone mexicana (left), A. × hybrida (middle) and A. ochroleuca (right), Sta. Cruz de La Palma, August 2014 (Photograph: R. Otto).

FIGURE 5. Argemone × hybrida, Sta. Cruz de La Palma, three vigorous individuals: overall view of a single plant (above), stem base (left) and newly sprouting stem base with dead basal branches (right), August 2014 (Photograph: R. Otto).