Morphometric and Reproductive Variation in the Strict Endemic Helichrysum Melitense in Gozo, Malta

Morphometric and reproductive variation in the strict endemic Helichrysum melitense in Gozo, Malta Joelene Xiberras1, Sandro Lanfranco1* 1Department of Biology, University of Malta, Msida, Malta *[email protected] Introduction: The strict island endemic Helichrysum melitense (Pignatti) Brullo, Lanfranco, Pavone & Ronsisvalle is restricted to rupestral habitats along the western coast of the island of Gozo, in the Maltese Archipelago (Fig.1). In spite of its conservation significance, there is little detailed information on the distribution, morphology and reproductive performance of this species. The present study, extending from February 2012 to April 2013, therefore aimed to characterise the following features of Helichrysum melitense: • Distribution; • Variation of leaf morphology across sub-populations; • Reproductive effort. Figure 3: Comparison of mean leaf length and mean leaf breadth in sub-populations of H.melitense and in H.rupestre (right). Data for H.rupestre (n=380) taken from Galbany-Casals et al. (2006). The table (left) lists the P values derived from pairwise comparisons in One-way ANOVA, comparing the leaf dimensions of the individual sub-populations and of the entire sample (n=983) of H.melitense with H.rupestre. Reproductive effort: Three plants from each sub-population were visited twice-weekly between February and July 2012. The number of new capitula and total number of capitula were determined during each visit during the flowering period (Fig.4). • Peak flowering rate was attained between 10 and 20 days after first flowering (Fig.5). A number of capitula were subsequently detached from the plants in August 2012 (Fig.4) and their flowers dissected, in order to investigate seed production. • The plant has relatively very low fertility; • Out of 4877 flowers that were dissected, 2836 (58.15%) had not set seed; • Only a small proportion (7.23%) of the seeds that formed were found to be potentially viable (Fig.5). Figure 1: Helichrysum melitense in flower at Tal-Port, Gozo, Malta. Distribution: The distribution of the species was determined through field surveys and through field confirmation of records in literature. • H.melitense is restricted to an area of less than 5km2 on rocky terrain along the coastal fringe of Western Gozo (Fig.2); • Five main sub-populations, ranging from 364 plants to 30 plants in size, were identified and . surveyed; • A number of sporadic clusters were also noted. Figure 4: Flowering (left), Fruiting (centre) and seeds (right) in H.melitense. Figure 5: Mean flowering rate in sub-populations of H.melitense (left) and comparison of the mean number of potentially viable seeds (PVS) and shrivelled seeds (SS) in each of the five sub-populations (right). Conclusions: Figure 2: Location of sub-populations (red polygons) and sporadic clusters (yellow markers) of • Although the habitat colonised by H.melitense is a Protected Area, the entire population is H.melitense in western Gozo. Location codes are as follows: HKA (Hekka); SLM (Ta’Slima); QWR small in size and highly localised and should therefore be considered vulnerable; (Qawra); PRT (Tal-Port); WRD (Wardija); GLQ (L-Ghalieqi); MXW (Ta’Maxwell); GRZ • Despite the low production of potentially-viable seed, the overall population size has not (Ta’Gruzzjal); GTG (Gebla tal-General); HRX (Ta’Harrux); XUR (ix-Xurbeb); TRT (it-Turretta). been observed to change significantly over the past thirty years, suggesting that this low fertility may nonetheless achieve replacement level for the species; • The sub-population at Hekka Point is distinct from the other four sub-populations in having longer and broader leaves, an important taxonomic criterion; Variation in leaf morphology: • The significant differences in leaf length and leaf breadth between H.melitense and H. Variation in leaf morphometry (leaf length and leaf breadth) was investigated by sampling 983 rupestre do not necessarily confirm H. melitense as a distinct species, as leaf morphometry plants from the five main sub-populations. is a highly variable trait across the genus Helichrysum. • Mean leaf length ranged from 5.45 ±0.78cm (Hekka) to 3.78 ±0.62cm (Qawra); • Mean leaf breadth ranged from 0.64 ±0.13cm (Hekka) to 0.46 ±0.09cm (Tal-Port); • Variation across sub-populations was greater than that within sub-populations for leaf length with such a trend not being observed for leaf breadth; References: • Comparison of leaf morphometry between H. melitense and Helichrysum rupestre, (within Galbany-Casals, M., Saez, L., & Benedi, C. (2006). A taxonomic revision of Helichrysum sect. which the Gozo populations were originally placed) showed a statistically-significant Stoechadina (Asteraceae, Gnaphalieae). Canadian Journal of Botany, 84, 1203-1232. difference between the two forms on the basis of leaf breadth and leaf length (Fig.3). .

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