Two Texas Toadshades

Trillium gracile, and T. ludovicianum may both be present in eastern Texas. These are my notes for distinguishing them from one another, taken from the monograph where John Freeman first described T. gracile and clarified the previously-hazy description of T. ludovicianum. Where metrics are given, I have omitted the extreme values, providing only the "typical" ranges (not in parentheses). Other Trillium also occur in Texas. By "leaves" I mean, technically, "bracts".

T. gracile T. ludovicianum
scape length : leaf length 3.2 - 3.5 2.4 - 2.8
shape elliptic
(elliptic-ovate to elliptic-oblong)
lanceolate or
broadly ovate
length 18 - 26 mm 24 - 40 mm
apex shape acuminate-blunt or obtuse acute or acute-rounded
length 21 - 35 mm 35 - 55 mm
anther sac
introrse latrorse
pollen color creamy - yellow olive - orange
anther connective
short-beaked short-rounded
carpel-height : stamen-length barely exceeding 0.5 ≥ 0.75
ovary x-section 3-angled 6-angled
stigma length 2.0 - 4.5 mm 4.5 - 10 mm
stigma attachment divergent
extending ovary outline into lyre-shape
initially continuous in outline with ovary
bending distal to point of attachment
outline smooth often prominently 6-ridged

I have seen comments suggesting that clump-formation and overall plant size differ between the two species, with T. ludovicianum being both more likely to form clumps and generally taller. These are not mentioned in Freeman's monograph. He gives an overlapping range of scape lengths for the two species, with T. gracile being actually taller on average (though it has petals that are about 2 cm shorter):

Trillium gracile: (16-) 20-32.5 (-36) cm long scapes
Trillium ludovicianum: (10-) 15-28 (-37) cm long scapes

Singlehurst et al. (2003) summarized the occurrences of Trillium in Texas. Changes from Freeman's monograph germane to their separation by morphology:

  1. T. gracile is listed as having elliptic to broadly ovate leaves.
  2. T. ludovicianum is listed as having clump-forming tendencies lacking in T. gracile

The two species are probably at least partially temporally isolated with T. gracile blooming later: late Mar -May vs. late Feb - early Apr.

Publicado el 11 de septiembre de 2018 por ddennism ddennism


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