Flora of North America species comparison

Grindelia squarrosa is probably native to the Great Plains and, perhaps, Rocky Mountain areas; it is widely introduced in other areas. Some plants are intermediate between it and G. hirsutula (i.e., between G. squarrosa and G. perennis, which has been treated as a variety of G. squarrosa). Plants of G. squarrosa with relatively narrow leaf blades (lengths mostly 5–8 times widths), mostly from the western part of the range of the species, have been treated as G. squarrosa var. serrulata. G. L. Nesom (1990i) and others have treated discoid plants included here in G. squarrosa as distinct (as G. aphanactis, G. nuda, and/or G. nuda vars. aphanactis and nuda); Nesom reported cypselae to be dimorphic in heads of radiate plants and monomorphic in discoid plants and noted that populations with discoid plants occur mostly south and west of populations with radiate plants. According to Nesom, plants of G. nuda with stems usually reddish (versus sometimes greenish), lengths of blades of mid-cauline leaves 4–10 (versus 1.5–4) times widths, and cypselae ± deeply furrowed (versus striate to shallowly furrowed) should be called G. nuda var. aphanactis.

Hybrids between Grindelia squarrosa (nuda) and G. arizonica have been recorded from Arizona and New Mexico.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 30 (18 in the flora).

The last attempt to account for the whole of Grindelia was by J. A. Steyermark (1934b). After comparing Steyermark’s treatment with specimens, one gets the impression that Steyermark had a keen eye for subtleties and trends in variation and that he sometimes assigned taxonomic ranks (species, variety, and forma) to trends rather than to what most botanists would consider to be taxa. Subsequently, writers of local and regional floras have felt obliged to recognize Steyermark’s “taxa.” Here, some of Steyermark’s “taxa” have been included within more broadly drawn circumscriptions; attention is called to them in discussions.

Within and among populations of grindelias, some morphologic traits appear to vary more from plant to plant than in most genera of composites. M. P. Dunford (1964) reported grindelias he had tested to be “essentially self-incompatible” and (1986) stated, “...Grindelia species are outcrossing and self-incompatible....” Some patterns of variation within Grindelia are similar to those found in genera characterized by apomictic seed production (e.g., local morphologic variants such as discoid plants in otherwise radiate taxa, hairy plants in otherwise glabrous taxa, narrow-leaved plants in otherwise broad-leaved taxa, etc.). See comments in discussion under 13. G. hirsutula.

References here to hybrids are based on observations by M. A. Wetter and/or on statements by M. P. Dunford (1964, 1986) and J. A. Steyermark (1934b).

Morphologic details and descriptive conventions for grindelias as treated here are:

Margins of most cauline leaves of most grindelias are usually dentate to serrate and have sharp, apiculate to setose teeth. Some species characteristically have cauline leaves with ± crenate margins and rounded, obtuse, or truncate teeth tipped by resin globules. Sporadically, individual plants may have some teeth resin-tipped and some teeth apiculate; such specimens may be hybrids or may indicate that the developmental paths to the two forms may be easily redirected. Plants with margins of some or all leaves entire may be encountered in almost all species of Grindelia and may predominate in some plants, populations, or species.

Leaf faces are usually gland-dotted with glands embedded in (or sessile in pits in) both the abaxial and adaxial epidermes. In some plants, populations, or species, the glands may be characteristically stipitate; developmental control for the different forms is apparently easily redirected (see comments under 11. Grindelia howellii).

Phyllaries are usually ± chartaceous proximally and herbaceous distally. Orientations of whole phyllaries and of their herbaceous apices are addressed in keys and descriptions. Individually, orientations of phyllaries vary from reflexed through spreading to appressed (often, within an involucre, outer phyllaries are ± reflexed and inner phyllaries are ± appressed). The herbaceous apices of phyllaries may be terete to flat and subulate to acuminate or acute, and vary from looped (coiled through ca. 270–400+ degrees), hooked (bent ± like a crozier through ± 180+ degrees), patent (bent at ± 90 degrees), or ± recurved or arcuate (sometimes incurved) to straight. An outer phyllary may be reflexed and have a looped, hooked, patent, recurved, or straight tip; an inner phyllary may be appressed and have a looped to hooked or recurved to straight tip; etc. The resin glands on the apices are usually circular, sometimes linear.

Cypselae of grindelias differ markedly from ovaries as seen at flowering. Cypselae are usually whitish or stramineous, sometimes brownish, grayish, reddish, or yellowish. They are usually ± compressed and ± ellipsoid to obovoid, sometimes 3–4-angled and ± reniform or rounded-prismatic. They are usually ± continuously variable in color, shape, size, and/or ornamentation within heads; sometimes they are ± dimorphic within heads, the outer differing from the inner in color, shape, size, and/or ornamentation. Cypselae that are 3- or 4-angled may have the angles ± thickened or ribbed. Apices of cypselae may be knobby (1–4 bumps or toothlike projections), coronate (a ± pronounced ridge), or smooth (rounded to ± truncate, not ornamented). Faces of cypselae may be smooth, striate (finely longitudinally nerved), ribbed, furrowed, or ± rugose (bumpy to tuberculate or with longitudinal and transverse fissures, grooves, or wrinkles).

Pappus elements are usually subulate scales (greatest width about 3 times thickness), setiform awns (greatest width about 2 times thickness), or bristles (width about equal to thickness) and are usually falling (± persistent subulate scales or setiform awns subtended by bristles in Grindelia ciliata). They may be ± straight or contorted to curled and may be smooth or barbellulate to barbellate; they were described as “entire” or “serrulate” to “setulose” by J. A. Steyermark (1934b) and others.

(Discussion copyrighted by Flora of North America; reprinted with permission.)