Myriophyllum rubricaule Valk. & Duist., 2022

Van Valkenburg, Johan L. C. H., Duistermaat, Leni (H.), Boer, Edu & Raaymakers, Tom M., 2022, Myriophyllum rubricaule sp. nov., a M. aquaticum look-alike only known in cultivation, European Journal of Taxonomy 828, pp. 1-15 : 4-8

Myriophyllum rubricaule Valk. & Duist. sp. nov.

urn:lsid:ipni.org:names:77299815-1

Fig. 1

Myriophyllum robustum auct. non Hook.f. Molecular Ecology Resources 13: 21–31 ( Ghahramanzadeh et al. 2013).

Myriophyllum brasiliense auct. non Cambess.: plants in trade.

Myriophyllum sp. trade name ‘brasiliensis’: Beringen R. 2020. — Pot R. et al. 2021. — Q-bank Invasive Plants. 2019–2021. — EPPO-Q-bank. 2022.

Diagnosis

Herba perennis aquatica vel paludigena. Folia omnia verticillata pectinata. Flores unisexuales, solae plantae femininae culturaeque cognitus. Flores intra axillas foliorum solitarii. Planta valde similaris Myriophyllo aquatico, sed caules foliaque modice, caules purpurei et folia emergentia virida. Flores feminei subrosei.

Etymology

The species epithet is based on the purplish red color of the stem.

Type material

NETHERLANDS • Grashoek , Roomweg 85, 5985 NS, Golf course Kapelkeshof; 51°22.0′ N, 5°56.5′ E; herbarium specimen; 13 Jul. 2009; fl; J.L.C.H. van Valkenburg & J. Hoogveld 3495; holotype: L!; isotypes: WAGPD[ WAG0453615 ]!, A!, BM!, BR!, MO!, NSW!; GenBank nos: MZ399148 (trnK3), MZ399140 (trnH-psbA), MZ399132 (rbcL), MZ399123 (matK), MZ401380 (ITS); SRA: ERR6000190 .

Additional specimens examined

NETHERLANDS • Wageningen , open air pond at PD ; herbarium specimen; originally from Wageningen, Garden Centre d’Oude Tol; 14 Jun. 2007; fl; J.L.C.H. van Valkenburg 3298; J.L.C.H. van Valkenburg det.; WAGPD[ WAG0453612 ]; GenBank nos: MZ399146 (trnK3), MZ399138 (trnH-psbA), MZ399130 (rbcL), MZ399121 (matK), MZ401378 (ITS); SRA: ERR6000191 • Vinkeveen , Aquaflora Vinkeveen , Ter Aase Zuwe , near junction main road Vinkeveen to Wilnis; herbarium specimen; cultivated at Wageningen, open air pond at PD, originally from Vinkeveen, collected 5 Apr. 2007; 9 Jul. 2007; fl; J.L.C.H. van Valkenburg 3314; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0453613 ] • herbarium specimen; grown by ‘ Simon van der Velde Waterplanten BV’, Albert van ‘t Hartweg 1, Bleiswijk; 30 Jul. 2007; J.L.C.H. van Valkenburg 3342; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0453614 ]; GenBank nos: MZ399147 (trnK3), MZ399139 (trnH-psbA), MZ399131 (rbcL), MZ399122 (matK), MZ401377 ( ITS); SRA: ERR6000192 • Wageningen , Garden Centre d’Oude Tol ; herbarium specimen; culta the Netherlands; 11 Apr. 2009; J.L.C.H. van Valkenburg 3472; J.L.C.H. van Valkenburg det.; L [ L 0767219 ; L 0909277 ]; GenBank no.: JX100590 (trnH-psbA) • Wageningen , Geertjesweg 15, Plant Protection Service ; herbarium specimen; culta, first received 1 May 2009 from Stoffels International BV, Maalbekerweg 14, 5951 NT, Belfeld, the Netherlands; 11 Sep. 2009; fl; J.L.C.H. van Valkenburg 3510; J.L.C.H. van Valkenburg det.; L [ L 0767220 ; L 0909323 ]; GenBank nos: JX100591 (trnH-psbA), JX100753 (rbcL) • Wageningen , greenhouse Plant Protection Service ; herbarium specimen; culta from plant obtained at garden centre; 28 Jul. 2011; J.L.C.H. van Valkenburg 3648; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0453609 ]; GenBank nos: MZ399149 (trnK3), MZ399158 (trnH-psbA), MZ399153 (rbcL), MZ399124 (matK), MZ401372 ( ITS); SRA: ERR6000195 • Hoogeveen , Kinholt; 52°43.34′ N, 6°26.00′ E; herbarium specimen; 5 Nov. 2018; J.L.C.H. van Valkenburg 3971; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0453559 ]; GenBank nos: MZ399159 (trnH-psbA), MZ399154 (rbcL) • Steenwijk , Het Eemter; 52°47.415′ N, 6°08.840′ E; herbarium specimen; 8 Sep. 2020; J.L.C.H. van Valkenburg 4116; J.L.C.H. van Valkenburg det.; WAG [ WAG.1971556 ], WAGPD [ WAG0452369 ]; GenBank nos: MZ399160 (trnH-psbA), MZ399155 (rbcL), MZ401381 ( ITS) • Hattem , Palmstraat; 52°27.768′ N, 6°04.428′ E; herbarium specimen; 8 Sep. 2020; J.L.C.H. van Valkenburg 4117; J.L.C.H. van Valkenburg det.; WAG [ WAG.1971558 ], WAGPD [ WAG0452378 ]; GenBank nos: MZ399161 (trnH-psbA), MZ399156 (rbcL), MZ401382 ( ITS) • Klazienaveen ; 52°44.580′ N, 7°00.615′ E; herbarium specimen; 7 Oct. 2020; J.L.C.H. van Valkenburg 4118; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0452243 ]; GenBank nos: MZ399150 (trnK3), MZ399141 (trnH-psbA), MZ399133 (rbcL), MZ399125 (matK), MZ401375 ( ITS); SRA: ERR6000193 • Wageningen , greenhouse NVWA ; herbarium specimen; culta, origin garden center more than 8 years ago; 8 Oct. 2020; J.L.C.H. van Valkenburg 4119; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0452240 ]; GenBank nos: MZ399151 (trnK3), MZ399142 (trnH-psbA), MZ399134 (rbcL), MZ399126 (matK), MZ401376 ( ITS); SRA: ERR6000194 .

HUNGARY • Borsod-Abaúj-Zemplén, Kács ; 47°57.44′ N, 20°37.00′ E; herbarium specimen; 20 Sep. 2019; A. Mesterházy s.n.; J.L.C.H. van Valkenburg det.; WAGPD [ WAG0452409 ]; GenBank nos: MZ399157 (trnH-psbA), MZ399152 (rbcL) .

Description

Dioecious amphibic or aquatic herb. Stem unbranched or with up to 6 branches per 20 cm, often rooting at submerged and lower emerged nodes; submerged part green to tinged red-brown and internodes 10–50 mm long; emerged part red or purplish red and internodes 3–25 mm long. Hydathodes few at base of submerged leaves, many at base of emerged leaves, ca 1 mm long, filiform, pale or reddish brown. Leaves in whorls of 4 or 5, pinnatifid with pinnae placed opposite and/or alternate. Submerged leaves 10–25(–50) × 3–10 mm, olive green or turning pale to dark reddish brown; pinnae 12–21, 3–14(–30) × 0.1–0.2 mm. Emerged leaves (7–)10–25 × 3–8 mm, bright green to bluish green, not glaucous, sometimes tinged red brown or pinnae red-tipped; pinnae (5–)7–21, 2.3–9 × 0.15–0.3(–0.5) mm. Flowers solitary in the axils of the emerged leaves, only female known, tinged pink. Pedicel 0.3–0.5 mm long. Bracteoles 2 at basis of pedicel, 0.5–1 × 0.1 mm, with 1–3 alternate and filiform lobes. Sepals 4, erecto-patent to reflexed, 0.5–0.7 × 0.2–0.3 mm, margin remotely fimbriate. Petals absent. Stamens absent. Ovary 4-sulcate, with 4 styles with feathery and more or less inrolled stigmas. Fruits unknown.

Amphibic herb with pinnate leaves in whorls of 4 or 5, only known from female plants and (escapes from) horticulture. Differs from M. aquaticum in its generally more modest dimensions, the stems being purplish red, the emergent leaves being green to bluish green and not glaucous (i.e., leaves without waxy coating) and the female flowers being pinkish ( Fig. 1 ).

Distribution

Origin unknown. Known from cultivation ( Netherlands, Belgium) and as escapes from cultivation since 2018 in the Netherlands (Hoogeveen, Steenwijk, Hattem, Klazienaveen) and Belgium (Maasmechelen, Houthalen-Helchteren, Brugge, Gent, Beauraing, Waimes; all confirmed from photographs at waarnemingen.be), and at least since 2019 in Hungary (Kács). It is unclear whether the observations in Belgium before 2018 (in retrospect the first observation dates from 2012; see waarnemingen.be records 70176185 and 95286205) refer to escapes or planted material.

Note

If grown in particularly nutrient rich and/or high light conditions plants develop much bigger submerged leaves (e.g., Valkenburg 3298 and 4116 WAGPD).

Similar species

Because both the submerged and emergent leaves are whorled, pectinate and not much different in length, and the inflorescence is emergent, the species fits in section Pectinatum M.L.Moody & D.H.Les. This section includes M. aquaticum and M. mattogrossense Hoehne ( Moody & Les 2010) . Myriophyllum aquaticum differs from M. rubricaule sp. nov. in having green stems only turning red when grown as a potted plant or in unfavorable conditions, but never purplish red, with leaves in whorls of 4–6, submerged leaves 25–45 mm long and green or red brown, emerged leaves 25–35 mm long and bluish green glaucous (i.e., with a waxy coating that can be rubbed of), and white flowers. Myriophyllum mattogrossense has green stems, small, globular, sessile glands on leaves and stems, submerged leaves 10–35 mm wide, and bisexual flowers ( Crow & Ritter 1999).

While performing the DNA barcoding study of M. aquaticum ( Ghahramanzadeh et al. 2013) , we initially thought that the plants described here as a new species belonged to M. robustum . This is a species resembling M. aquaticum with similar emergent pectinate leaves and solitary axillary flowers. However, M. robustum is described as having hermaphrodite flowers whereas M. aquaticum is dioecious ( Orchard 1980). Shortly after our paper was published, plants of M. robustum were received from New Zealand and were grown in a greenhouse. The cultivated plants had more robust erect emergent stems that were pink in the upper part, and subglaucous leaves that were oblong in outline with an acute tip. Surprisingly, the plants produced only female flowers in the greenhouse (Valkenburg 3739 WAGPD). Grown outdoors in a mesocosm in later years, the plants first produced female flowers, a row of hermaphrodite flowers and then, distally, male flowers (Valkenburg 3853 WAGPD).

Distinguishing molecular features of Myriophyllum rubricaule sp. nov.

As described above, M. rubricaule sp. nov. is morphologically distinguishable from M. aquaticum . Moody & Les (2010) described two specimens, M. sp. ‘red 1’ and M. sp. ‘red 2’, that were morphologically and genetically related to M. aquaticum . We made a molecular comparison of M. rubricaule , M. aquaticum , M. sp. ‘red 1’ and M. sp. ‘red 2’ using the same molecular markers ( Moody & Les 2010), namely the nuclear locus ITS (partial 18S, ITS1, 5.8S, ITS2, partial 28S), and the chloroplast loci trnK3 and matK to find out how M. sp. ‘red 1’ and M. sp. ‘red 2’ relate to M. rubricaule ( Figs 2–3 ). We included Myriophyllum heterophyllum Michx. and Laurembergia tetrandra (Schott) Kanitz as more distantly related species within the Haloragaceae in this comparison.

Based on ITS ( Fig. 2 ), all M. rubricaule sp. nov. specimens showed 100% sequence similarity. Myriophyllum sp. ‘red 1’ was most similar to M. rubricaule sharing 98.62% sequence identity. We only observed differences in the ITS1 sequence (38–42delCCCCG and 87delG). Interestingly, the specimens of M. aquaticum group with M. sp. ‘red 2’, albeit with a relatively low confidence value, sharing 96.27% and 93.65% identity with M. rubricaule , respectively.

The trnK3 and matK loci were extracted from the sequence data and subsequently concatenated, before tree generation. Similarly to ITS, the trnK3-matK sequences were identical for all samples of M. rubricaule sp. nov. ( Fig. 3 ). Intriguingly, the M. sp. ‘red 2’ and M. aquaticum JL 8405 trnK3-matK loci were identical to M. rubricaule . Myriophyllum aquaticum JvV 3494 and TP 3977 showed 99.88% similarity with M. rubricaule and M. sp. ‘red 2’ with only two single nucleotide polymorphisms (SNPs; T32A and T1243A). Myriophyllum sp. ‘red 1’ differs on 10 positions with M. aquaticum , M. rubricaule and M. sp. ‘red 2’ sharing 99.63% similarity.

Finally, we compared two other well-known chloroplast loci, rbcL and trnH-psbA, to identify more distinguishing molecular features between M. aquaticum and M. rubricaule sp. nov. We incorporated previously described sanger sequences ( Ghahramanzadeh et al. 2013) as well as newly generated sanger and Illumina sequences in the comparison (Supp. file 1 and 2). For trnH-psbA, all 12 specimens of M. rubricaule were identical to each other. Seven out of eight M. aquaticum were identical, for M. aquaticum JL 8405 we observed one SNP (G230A) (Supp. file 3). However, for two samples of M. aquaticum not all sanger data could be resolved resulting in two ambiguities: M188A for M. aquaticum JvV 3329 and K255T for M. aquaticum HD 426. A clear distinction was observed towards the 5’-end of the trnH-psbA intergenic spacer (nucleotides #237–292) where 13 SNPs were identified between the specimens of M. aquaticum and M. rubricaule resulting in approximately 96% similarity. Interestingly, we did not find any differences between M. aquaticum and M. rubricaule rbcL sequences (Supp. file 4). Even the distantly related plant species L. tetrandra shared 97.29% of rbcL identity. In contrast, for trnH-psbA, only a ~ 69–73% identity score was observed between L. tetrandra and M. rubricaule and M. aquaticum .

Figures

Fig. 1. Plants, prior to collection, of M. rubricaule Valk. & Duist. sp. nov. (Valkenburg 3495; red stem) growing amidst M. aquaticum (Valkenburg 3494; green stem) in an artificial pond at a golf course, illustrating the more modest dimensions and color differences (13 July 2009, Grashoek, the Netherlands).

Fig. 2. Maximum likelihood tree based on ITS (partial 18S, ITS1, 5.8S, ITS2, partial 28S) sequences. The Tamura 3 parameter model was used (Tamura 1992). The tree with the highest log likelihood (-1398.71) is shown. Bootstrap values after 1000 replicates are expressed as percentages.A discrete Gamma distribution was used to model evolutionary rate differences among sites (5 categories (+G, parameter = 0.4031)). The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Laurembergia tetrandra AP 33 was used as an outgroup.

Fig. 3. Maximum likelihood tree based on concatenated trnK3-matK sequences. This tree was inferred by using the Maximum Likelihood method and Tamura 3 parameter model (Tamura 1992). The tree with the highest log likelihood (-2853.86) is shown. Bootstrap values after 1000 replicates are expressed as percentages. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Laurembergia tetrandra AP 33 was used as an outgroup.