Subspecies of Mibora minima in Britain
Subspecies of Mibora minima (L.) Desv. (Early Sand-grass) in Britain MICHAEL WILCOX
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ometimes described as the smallest grass in the world, Mibora minima (Early Sand-grass) is a rare grass in Britain, which may be overlooked due to its early flowering time. A study on European plants concluded that some populations from the NW Iberian Peninsula were separable as M. minima subsp. littorea. In Britain, plants from Anglesey and North Uist have been considered to be like subsp. littorea, with most other colonies in Britain belonging to subsp. minima. The plants examined in this study, from several colonies including those from Anglesey, were essentially found to be within the range of subsp. minima. It is without doubt M. minima is a very small grass indeed, and perhaps considered to be the smallest grass in the world (see Rich, 1997), though other species can be as small in some forms (e.g. Poa infirma Early Meadow-grass) and certainly some of the parts of M. minima (such as stomata and anthers for example) are much larger than those in species such as P. infirma. Ortiz et al. (1999) studied Mibora minima across populations in Europe (including some from Britain) and concluded that there is a taxon that has measurable differences to the usual form. This was separated at subspecies level (subsp. littorea (Samp.) S. Ortiz, J. Rodrígeuz-oubiña & P. Guitián) and is only known from the NW Iberian Peninsula (Ortiz et al., 1999). It is now accepted as a subspecies in Flora iberica (Castroviejo, 2021). Some populations in Britain have been studied in terms of their distribution at a local scale (see Smith, 2005; 2007; Smith et al., 2011; Smith et al., 2015). However, few have been considered as one subspecies or another. In Britain, Cope & Gray (2009) state (based on Ortiz et al., 1999) that plants from Anglesey belonged to M. minima subsp. littorea. Specimens from North Uist (v.c. 110) have also been identified as subsp. littorea (Smith et al., 2015).
Essentially, Mibora minima is a species where each spike is a one-sided raceme of one or two rows of spikelets. In essence, it was separated as subsp. littorea (Ortiz et al., 1999) based on the following (main) characteristics: Spikelets (2.2)2.5–3.5 mm (maximum 4 mm) – not 1.7–2.5 mm (maximum 3 mm) Spikelets in two rows where the 1st and 3rd overlap (and most subsequent rows) such that spikelets appear in two rows side-by-side (with a biseriate appearance from the front) – not a single row where the 1st and 3rd do not overlap (spikelets more or less with a uniseriate appearance; there is some overlap between the two subspecies [see Ortiz et al., 1999]). Essentially, subsp. littorea has larger, overlapping spikelets which appear in two rows compared to the smaller spikelets in a more or less single row (not overlapping) in subsp. minima. Subsp. littorea is also said to have the basal pedicel of the inflorescence conspicuously rugose (being slightly rugose or smooth in subsp. minima). More technical data on adaxial and abaxial cell shapes and sizes is given in Ortiz et al. (1999) in which (using absolute extreme values) the cells are clearly larger and more rectangular at the adaxial leaf surface in subsp. littorea. Plants from several colonies from Britain were examined to see if any fit the description of subsp. littorea. Being rare this was limited to ten or fewer plants but with more than five spikes per plant. North Bull, Dublin: These plants were clearly like M. minima subsp. minima with primarily onesided racemes. They have pollen with the average size of 20 µm (appears not to have been measured in Ortiz et al. [1999] but plants of both subspecies were said to be diploid, 2n = 14). The lemma (c. 1.4 mm) has long hairs to about 0.5(6) mm. Glumes 2.5–2.7 mm; the apex is truncate and frayed; the BSBI NEWS 148 | September 2021
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