84
DAVID D. KECK
tionary patterns. For the most part the generic lines are distinct and the
species clear-cut. Only some of the highlights of the experimental work
with this subtribe have been published (Clausen et al. 1932, 1933, 1934,
1935, 1936, 1937, 1940b, 1941, 1942, 1943, 1944, 1945; Clausen, 1951).
The genus Layia received a somewhat more complete cytogenetical
analysis than the others in the subtribe, and so it illustrates well the application of such data to a taxonomic problem. Fifteen groups meet the
requirements of the taxonomist and the experimentalist for species. This
number is not out of line with earlier taxonomic treatments (the latest
of these recognized 14 species), but the line-up of the species is noticeably changed. Of the previous 14, only 10 are now recognized as bona
fide species of Layia, 3 having been reduced to synonymy and 1 transferred to another genus. But the 5 new ones include 3 previously undiscovered in nature, and 2 that cytological and genetical data indicate
must be recognized as equally distinct as any other.
This genus is composed of spring-flowering annuals all native to, and
all but two confined to, California. The species with the widest distribution, L. glandulosa (Hook.) Η. & Α., extends from Washington and Idaho
to Lower California; four other species are very restricted endemics:
L. jonesii Gray, extending a very few miles along the San Luis Obispo
coast, L. leucopappa Keck, known only from a few square acres at the
head of the San Joaquin Valley, L. carnosa (Nutt.) T. & G., occupying
four or five widely scattered short stretches of coastal sand dunes from
Humboldt County to Santa Barbara County, and L. discoidea Keck,
known from a single hillside in San Benito County.
Morphologically these fifteen species are distinguishable without too
much difficulty. Twelve stand out rather boldly from each other, with
many good morphological characters; the other three offer some opportunity for confusion, L. septentrionalis Keck looking superficially similar
to a subspecies of L. glandulosa and a common variant of L. platyglossa
(F. & M.) Gray, L. paniculata Keck differing principally by quantitative
characters from L. hieracioides
(DC.) Η. & Α., and L.
pentachaeta
Gray ssp. albida Keck looking quite similar to L. glandulosa.
The
several species differ from each other in the amount of their variability,
the restricted endemics being notably uniform; but the most variable
species, L. gaillardioides
(H. & A.) DC, has a smaller range than either
L. glandulosa or L. platyglossa.
Cytologically, 6 species have 7 pairs of chromosomes, 8 species have
8 pairs, and 1 species as 16 pairs. These numbers were safely established by counts from several populations. The degree of homology
between the chromosomes of the different species differs, as determined
DAVID D. KECK
tionary patterns. For the most part the generic lines are distinct and the
species clear-cut. Only some of the highlights of the experimental work
with this subtribe have been published (Clausen et al. 1932, 1933, 1934,
1935, 1936, 1937, 1940b, 1941, 1942, 1943, 1944, 1945; Clausen, 1951).
The genus Layia received a somewhat more complete cytogenetical
analysis than the others in the subtribe, and so it illustrates well the application of such data to a taxonomic problem. Fifteen groups meet the
requirements of the taxonomist and the experimentalist for species. This
number is not out of line with earlier taxonomic treatments (the latest
of these recognized 14 species), but the line-up of the species is noticeably changed. Of the previous 14, only 10 are now recognized as bona
fide species of Layia, 3 having been reduced to synonymy and 1 transferred to another genus. But the 5 new ones include 3 previously undiscovered in nature, and 2 that cytological and genetical data indicate
must be recognized as equally distinct as any other.
This genus is composed of spring-flowering annuals all native to, and
all but two confined to, California. The species with the widest distribution, L. glandulosa (Hook.) Η. & Α., extends from Washington and Idaho
to Lower California; four other species are very restricted endemics:
L. jonesii Gray, extending a very few miles along the San Luis Obispo
coast, L. leucopappa Keck, known only from a few square acres at the
head of the San Joaquin Valley, L. carnosa (Nutt.) T. & G., occupying
four or five widely scattered short stretches of coastal sand dunes from
Humboldt County to Santa Barbara County, and L. discoidea Keck,
known from a single hillside in San Benito County.
Morphologically these fifteen species are distinguishable without too
much difficulty. Twelve stand out rather boldly from each other, with
many good morphological characters; the other three offer some opportunity for confusion, L. septentrionalis Keck looking superficially similar
to a subspecies of L. glandulosa and a common variant of L. platyglossa
(F. & M.) Gray, L. paniculata Keck differing principally by quantitative
characters from L. hieracioides
(DC.) Η. & Α., and L.
pentachaeta
Gray ssp. albida Keck looking quite similar to L. glandulosa.
The
several species differ from each other in the amount of their variability,
the restricted endemics being notably uniform; but the most variable
species, L. gaillardioides
(H. & A.) DC, has a smaller range than either
L. glandulosa or L. platyglossa.
Cytologically, 6 species have 7 pairs of chromosomes, 8 species have
8 pairs, and 1 species as 16 pairs. These numbers were safely established by counts from several populations. The degree of homology
between the chromosomes of the different species differs, as determined