Sporobolus aff. fertilis (Steud.) Clayton (1965: 291)

Verloove, Filip, Gonçalves Silva, Juan J. & Leliaert, Frederik, 2024, Critical notes on grasses (Poaceae) of Madeira, Portugal, Phytotaxa 670 (1), pp. 1-17 : 6-7

Sporobolus aff. fertilis (Steud.) Clayton (1965: 291)

[syn.: Sporobolus indicus (L.) R. Br. var. major (Buse) Baaijens ]

Specimens examined: PORTUGAL. Santo da Serra [popular short name for Santo António da Serra; FV], champ cultivé à l’abandon du village vers Porto da Cruz, 15 July 1977, E. Jacques 10796 ( BR, dupl. TAIF) ; Matur [in fact, this probably refers to the same locality as the previous collection, since both collections were made during the same expedition to Madeira; FV], 300 m alt., bord du chemin, July 1977, L. Delvosalle s.n. ( BR) ; São Jorge, R101 road near village center, roadside, ca. 30 individuals, 15 September 2021, F. Verloove 14625 ( BR) ; Santa Cruz, drive out of VR1 motorway near airport, lawn weed, very common, ca. 500 individuals, 23 September 2021, F. Verloove 14647 ( BR) .

The Sporobolus indicus complex is a taxonomically challenging group (e.g. Clayton 1965, Baaijens & Veldkamp 1991, Simon & Jacobs 1999). Plants from this complex that are naturalized in the island of Madeira are at present usually ascribed to S. africanus (Poir.) Robyns & Tournay (syn.: S. indicus var. capensis Engl. ) ( Press & Short 1994, Vieira 2002, Jardim & Sequeira 2008, Menezes de Sequeira et al. 2012). The first records, however, were published as S. indicus ( Hansen 1971) . These two species are morphologically very similar and not easily told apart. During our recent field work, another member from this complex was observed. Compared to the two aforementioned species, these plants stand out for being significantly taller, with stems easily exceeding 100 cm in length, inflorescences with slightly patent lowermost branches up to 50 mm long and small spikelets (up to 2 mm long) and sometimes only 2 (vs. usually 3) anthers. For its tallness, inflorescence shape and anther number, these plants mostly resemble S. fertilis . The latter shows some resemblance to the Australian weed S. elongatus R. Br. and both species have often been confused (e.g. Yang 1987, Baaijens & Veldkamp 1991).Yet, these species are not related: S. elongatus is not a member of this complex and its placement in fact remained unresolved in a recent molecular phylogenetic study ( Peterson et al. 2014). S. elongatus has shorter (up to 20 mm long), more patent and distant lower panicle branches. Most recent studies in fact have shown that S. fertilis is most closely related to S. africanus ( Shrestha et al. 2003, Shrestha et al. 2005, Peterson et al. 2014). These two species have the position of the grain vs. lemma and palea in common: the lemma and palea exceed the grain by up to its own length, gaping widely open beyond its top ( Clayton 1965), which apparently is an important synapomorphy.

Given the complexity of the group, we also genetically analyzed the Madeira plants (collection F. Verloove 14647) based on ITS and matK DNA sequence data ( Figure 2 ). The matK sequence was identical with sequences labelled as Sporobolus fertilis ( M. W. Chase 19305 from K) and S. indicus ( M. W. Chase 9275, also from K), both obtained from cultivated material of uncertain provenance, as well as a sequence labeled as S. indicus from Brazil ( USDA-NPGS PI 310309), and a sequence labeled as S. africanus from mainland Portugal ( BM 2008/148). The ITS sequence was identical with two sequences of S. jacquemontii Kunth [syn.: S. pyramidalis P. Beauv. var. jacquemontii (Kunth) Jovet & Guédès ] from Mexico ( P. M. Peterson 15902 & J. Valdes-Reyna from US and Estrada 18964 et al. from CIIDIR), and was closely related to sequences of S. berteroanus , S. indicus , S. pseudairoides and S. fertilis from various (sub)tropical locations ( Peterson et al. 2014). In general habit, S. jacquemontii certainly shows some resemblance to the Madeira plants but it is readily and unequivocally distinguished based on floral details: in the plants from the island of Madeira, the upper and lower glume are very unequal in length (respectively ca. 1–1.5 and 0.5 mm long) and the upper glume is acute at apex and at least ½ as long as the spikelet (ca. 55% as long). In S. jacquemontii , in contrast, the upper glume is only slightly longer than the lower and the upper glume is erosely truncate at apex and less than ½ as long as the spikelet. It usually also is a smaller plant, much unlike the tall plants observed in the island of Madeira. Examination of reliably identified herbarium material in BR confirmed that S. jacquemontii is not a good match for the Madeira plant.Therefore, it is here tentatively assigned to S. aff. fertilis . Sporobolus fertilis is native to tropical and subtropical southeast Asia. It was trialed as a pasture species in Australia and now has become a very noxious weed there (Giant Parramatta grass; very numerous online references); it is, moreover, resistant to particular herbicides ( Harrington & Ghanizadeh 2024). It is also naturalized in some South Pacific islands ( Clayton & Snow 2010). Plants from the S. indicus complex that are naturalized in southwestern Europe since the 20 th century were initially ascribed to this species ( Jovet & Guédès 1968), erroneously so, as pointed out by Veldkamp (1990). According to the Euro+Med Plantbase (2023), S. fertilis is not known from Europe and the Mediterranean area. However, it is locally naturalized in Turkey ( Byfield & Baytop 1998, Uludağ et al. 2017) and even considered to be an invasive (transformer) species in the Caucasus ( Kolakovsky et al. 1990, Lytvinskaya & Abdyeva 2021). As far as Madeira is concerned, S. fertilis appears to be a locally naturalized species. A small roadside population was recorded in São Jorge in September 2021 and an impressive stand was found in a lawn next to the airport in Santa Cruz, also in September 2021. Interestingly, this species was already collected in the island of Madeira in the 1970’s (as S. indicus ), in Santo da Serra (see Specimens examined). Thus, it probably has been present for about half a century, yet is less common than the other representatives of this complex in Madeira, viz S. africanus and S. indicus .

Figures

FIGURE 2. Maximum likelihood trees (IQ-TREE) inferred from nuclear rDNA internal transcribed spacer (ITS) region and the plastid encoded matK gene, showing the position of the Sporobolus aff.fertilis specimenfrom Santa Cruz (F.Verloove 14647, BR0000027058626V, ENA/GenBank accessions). Values at branches correspond to UFBoot2 supports (1000 replicates).Scale represents estimated substitutions per site.