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12.1 All measurements are metric, but the unit decimetre (dm) is not to be used. For most structures, millimetres are the smallest units to be used (e.g., "anthers 1.2--2 mm"), but for some structures, such as pollen or spores, it may be appropriate to use micrometers (e.g., "pollen 5--10 µm in diam.").
12.2 For single measurements "ca." or "to" precede the measurement (e.g., "trees ca. 10 m tall" and "ovary to 2 mm"). Single numbers for quantitative characters are often exact so usually will not use "ca." (e.g., "stamens 10").
12.3 When a single measurement is used, the measurement indicates length, unless some other dimension is explicitly stated, and the word "long" will not be added (e.g., "filaments ca. 3 mm" rather than "filaments ca. 3 mm long" but use "stem ca. 5 mm in diam."). In the case of tree diameter use "d.b.h." for diameter at breast height, which is measured at 1.4 m above the base, rather than "diam."
12.4 If a range of measurements is found for a taxon, a double dash separates the measurements which is changed to an en dash (–) during formatting (e.g., "leaf blade 3--5 cm"). However, a single dash (hyphen) is used to separate a numbers from the words they describe (e.g. "style 3--5-lobed").
12.5 Exceptional measurements are given in parentheses (e.g., "petiole 3--5(--7) cm"). However, do not use parentheses to indicate exceptional conditions for descriptive terms (e.g., do not use "leaf blade lanceolate (to ovate)" but use "leaf blade lanceolate to rarely ovate").

12.6 If two discontinuous alternate states are commonly found in a taxon, the states are separated by the word "or" rather than a double dash (see also paragraphs 12.6 and 12.7) (e.g., "stamens 5 or 10" and "petals 4 or 5"). Parentheses can also be used to express alternate states where such states are exceptional (e.g., "stamens 5(or 10)" and "style (3 or)4-lobed").

12.7 If both length and width are used, the measurements are given as length times width, and the same units are generally used for both (but see paragraph 12.8). For a times sign use a capital X with a space before and after the X (e.g., "leaf blade 4--6 X 1--3 cm" and "sepals ca. 4 X 1 mm"). During formatting, the capital X will be changed to a multiplication sign (×).
12.8 Use units appropriate to the scale of the measurements. If a measurement would be an integer or an integer plus a decimal fraction at the next higher or lower unit, then the next higher or lower unit should be normally be used (e.g. 30 mm becomes 3 cm). Millimetres would normally be used for measurements up to 20 mm. Round off to the first decimal place (e.g., "3.53 cm" becomes "3.5 cm" and "4.15 mm" becomes "4.2 mm"). When a range includes a value above 20 mm then cm should be used as the units for all values (e.g., "8--25 mm" becomes "0.8--2.5 cm"; "1.8--1.9 cm" becomes "18--19 mm"; 7--12 mm" does not change).

This should only apply when both sides of an X statement include values above 20 mm (e.g., "8--12 X 9--12 mm" does not change, "0.8--2.5 cm X 9--12 mm" becomes "8--25 X 9--12 mm"; "8--25 X 9--22 mm" becomes "0.8--2.5 X 0.9--2.2 cm"). However, when X is used and the length and width are more than two orders of magnitude different, use different measurements for the length and width (e.g., use "20--30 cm X 0.5--1 mm" rather than "200--300 X 0.5--1 mm").
12.9 The following shows additional examples of the style that will be used and will not be used:
ovary (1--)3--5(--6) mm not ovary (1--) 3--5 (--6) mm
leaf blade ca. 5 X 1--2 cm not leaf blade 5 X 1--2 cm
leaf blade ca. 5 X 2 cm not leaf blade ca. 5 X ca. 2 cm
leaf blade 2--5 X ca. 2 cm not leaf blade ca. 2--5 X 2 cm
petiole 3.5--7 mm not petiole 3.5--7 mm long
trees 10--15 m not trees 10--15 m tall
shrubs 30--70 cm not shrubs 3--7 dm
2-lobed not bilobed
2-cleft not bifid
nutlets 2 or 3 not nutlets 2--3
(3 or)4(or 5)-carpellate not (3 or) 4 (or 5)carpellate
3--6(or 7)-hooked not 3--6 (or 7)-hooked
5(--7)-parted not 5--(--7)parted
2(or 3)-lobed or lobes 2(or 3)
(5 or)6-veined or veins (5 or)6
4- or 5-valved or valves 4 or 5
4--6-valved or valves 4--6
(5--)7-ribbed or ribs (5--)7
3(--5)-sided or sides 3(--5)